2025 Update:
A year later the camera is still super, but with the new phone (again Android) it DOES NOT connect at all! I have tried all the tricks (including the one that worked on the old one), and just nothing. With a cable to the phone it also generally doesn't connect, so I have to wait to get back to the computer to transfer the photos. It's really stupid that the app from a big company like DJI is so bad and unreliable... However, the camera itself as a device has been very convenient for me.

5⭐ camera / 1⭐ app.

2024 Version:
I was reading about this camera for several days before I bought it and it is exactly as described! The build quality is very good, it feels very nice in my hand. It is indeed very tiny, even for me who has small hands. Exactly what I wanted! You wear it under your shirt with the magnetic necklace and it's like it's not even there.

The battery lasts as they say, that is, not very long, but given the size it's acceptable. It has a smart mode so you don't waste battery, where you have the camera completely off and when you press the button, it turns on and immediately starts recording video. After a few seconds it can also turn off automatically so it doesn't drain your battery while you're not recording. In general, you have many settings and you can make it behave exactly as you want.

Most of the negative comments I see have to do with the fact that it can only shoot 4K for a few minutes at most. This doesn't bother me, because firstly I'm not interested in shooting 4K, and secondly it's clearly stated on DJI's website, so it wasn't a surprise... However, I agree that it's very misleading to call it a "4K camera" in the title given this!

I don't do action sports, I just wanted it so I could easily take videos on vacation or when I'm skating, because it's not convenient at all to have to take your phone out of your pocket and have your hands constantly busy. With this camera you can live in the moment and take videos!

THE ONLY NEGATIVE is the app! For days I couldn't get it to work (I tried both Android and iOS). I followed DJI's instructions, but it wouldn't connect at all. In the end, I had to go against the official instructions and connect directly from the phone's Wi-Fi settings. I also had to turn off auto connect on all available networks AND in the general phone settings turn off the option that lets the phone choose the best network on its own. This is because the camera presents itself as a hot spot that the phone must connect to. But the phone detects when a network doesn't actually provide internet access and disconnects you! Really a very dumb way! At least with a cable, as soon as I connected it to the MacBook, it recognized it immediately.

Apart from the initial connection problem, the app is very bad. It freezes incredibly on Android. Overall, I would say that the camera is amazing and exactly what I wanted, but the app is so bad that I have to take off one star.

I have it for 3 months. I record videos with a card. I have it on a helmet. It captures video very well, including sound and vibrations. It is not small because if you add the power module, it is like a GoPro. If you shoot without the power module, the battery life is very short. The problems are elsewhere. First, for everything I will say below, I have noticed in these 3 months with completely amateur use. I have no knowledge about photography, etc. And I believe this is important for most people to be able to use it.
First, the camera claims to be 4k. The maximum you can shoot with 4k is 5 minutes of video. Then it stops due to overheating and you are left with nothing. Each setting, 2.7k, 1080, etc., can only shoot for a specific amount of time due to overheating. This cannot be fixed with the power module or the case. Because that's what DJI told me. With 2.7k and 30 fps, it can shoot for about 20 minutes before overheating. That is for me the second and most important downside. Up to 4gb, the video comes out intact. When it exceeds 4gb in capacity, then a video, for example, 20 minutes long, if you manage to shoot it with 2.7k 30fps, it will be cut into 8 videos when you download them, each lasting 3 minutes and 800mb. If you want to make it into one video as it was originally through the DJI mimo app. However, when you make another video, you have the option to make it 720p or 1080p (with the application). So you lose the 2.7k or 4k. If you want to have better quality, then you download a program to play the director and do editing. Unacceptable for me. I will change it and get a GoPro even if it is more expensive.

Owner of the Action 2 here for 7 months, recently in August I did its first serious test in adverse but reasonable vacation conditions.
So far, my opinion is that the camera is excellent for many reasons that I will mention below.
Firstly, if you want an action camera for extreme sports such as surfing, skydiving, skiing, but even for timelapse on a motorcycle, then I recommend the GoPro for you or the Action 1.
Beyond that, for anything else, I recommend the DJI without hesitation.
It is the ultimate incognito travel kit to comfortably capture all your moments on a trip, without difficulty in transportation, always in your pocket. Not that it can't do extreme sports, it's just definitely more fragile than a GoPro and it wasn't originally designed for that use (they had vlogging more in mind).

Positive elements after vacation:

-The most useful mounts, apart from the tripod head, are definitely the necklace, mainly for transporting the DJI, so you can always have it around your neck wherever you go and ready for shooting. The magnet is very strong and doesn't come off in normal conditions. Especially on vacations where you often may not have pockets or are holding things, it's the best thing, you have it around your neck and whenever you see something, boom, you capture it.

-Amazing battery, it never runs out in a whole day, and simply every time you're not using the camera mount (or the battery mount you have), you attach it to the bottom body and put it in your pocket, and it's back to 100% until you take it out again.

-Now, the overheating issue that received a lot of hate on its release, under normal conditions you will never have a problem (it has never overheated for me, by the way). Now, if you set it to record video at 60 and 120 FPS below 40 degrees Celsius under the Greek sun, even you would overheat. In any other conditions, especially in a situation underwater (where the camera is completely waterproof), it has absolutely no problem. Something extra is that sand doesn't stick to it at the beach due to its construction material. (It's good to have only the camera out at the beach and attach it to the battery module when you return home or after rinsing it in a tap).

-My way of using it was to have a memory card (64GB) in the battery mount, so as soon as I returned from the beach or a walk, I automatically transferred all my files from the camera to the SIM card. So on the next outing, I had 22 free GB to use until the evening. Generally, it had enough space. For 10 days of vacation on 2 islands, it was more than enough. (The clips I shoot don't exceed 1-2 minutes, and most are 10 seconds). If someone needs more, they can simply get a larger SIM card.

-Low light. The low light performance of the DJI is very good compared to other action cameras, and even the stabilization is good without producing strange artifacts, but remember to set it to 60fps, otherwise the shakiness is noticeable at 24 and 30fps. From the moment you lock the exposure at a maximum of 1600 ISO, it won't produce much noise.

-Now, for the sound, the DJI has a very strong point, especially if you have the 3 microphones. Specifically, for the parts where I want to speak clearly to the camera, I have attached a Saramonic USB mic that works very well with the Action 2. The microphones themselves do a good job, and you need the 3 of them more for sound direction than for extra quality.
The other solution I found and is an excellent choice was to get a Samsung USB-C male to 3.5mm female adapter and attach a luv mic to the DJI. Excellent sound performance.

A top camera in its category. Competitors are only the GoPro 9 & 10.
The camera comes in two bodies. One is the waterproof body of the camera with internal memory of 24GB and a battery life of 60-90 minutes. The second body is the extra battery with a duration of 180 minutes. In the second body, we have a charging/microphone port and a memory card slot. Finally, in the package, you will find the pendant necklace to wear it on your chest. And the mount to attach it to a pole, tripod, etc.
In the positives:
-Quality metal construction.
-Excellent video quality.
-With a starting price of 270 when its competitor is twice the price.
-Supported by DJi.
-The pendant necklace allows you to hang it on your chest and shoot in museums, on the street, on walks, in sports activities without needing extra accessories.
-It has many effects and the ability to record in 4K.
-Very good application for mobile phones.
-Can also function as a webcam for PCs.

In the negatives:
-Its lens is not detachable, so if it breaks or cracks, it renders the camera useless.
-The battery is internal, so as time passes, its performance decreases and you cannot replace it.
-Its accessories are a bit hard to find and expensive.
-In underwater shots, it is limited in battery life and video duration since the second body is not waterproof.
-In 4K at 20-30 minutes, it overheats and shuts down, but after contacting DJI, they send you a free case that reduces its temperature.
-The budget version has a small screen, which may make it difficult for some in selfie videos or vlogs... but the application on your smartphone provides the framing, so it solves the problem relatively easily.

However, it is still a top choice. Check out our unboxing video presentation here:
https://www.youtube.com/watch?v=LaYzIHhIV7Q&t=389s

P.S. In the overheating issue, DJI provides the Magnetic Protective Case completely free of charge. For more information, watch the related video:
https://www.youtube.com/watch?v=QlCVKpJFXOg&t=5s

With the discount, the price/value ratio makes it the top choice. I use it either on the motorcycle or for underwater shots. The video quality is excellent. I would like the photo quality to be slightly better. The stability of the video, despite the vibrations, is more than impressive. It attaches and detaches easily with the magnetic system, and its attachment is perfectly secure. It is very practical to use it as a chest mount. It only overheats when it remains still. In in-car recording, mounted with a suction cup on the windshield, with an external temperature of almost 40C, it heated up and stopped recording after 4 minutes. In the same spot with an external temperature of 28C, it stopped recording when its storage capacity was exhausted. The build quality is much higher than the competition. I preferred the combination with the power module for maximum battery life. Be careful with aftermarket magnetic attachments. They are of good quality, but they require a double check to ensure they are properly attached. It takes a little getting used to not photographing your fingers. I am preparing to buy a second one, and I still haven't decided whether it will be the Action 2 or Action 3.