It is an action camera, which means it is made for outdoor activities, however I tried it for the first time at a live DJ event.
Relatively low lighting in the venue.
Good filming quality.
It shoots in 4K but if you edit on the mobile app and don't have much space then it drops to 1080.
There is noise at 1080.
I haven't seen it yet at 4K.
Quality sound.
Battery lasts 2 hours.
The live event lasted 6 hours so I changed 3 batteries.

Now for the files.
The files are in insta360 format, which means they are not automatically mp4, so you choose the frame you are interested in and export it to mp4 or via computer you select the 360 option so you have 360° video.
The latter works a lot in many videos on the internet because viewers probably like to have a full 360° view.

For those who want the simple conventional frame like other action cameras, you need to select the frame you are interested in first and then get an mp4 file.

I didn't see this detail in any video showing you how to edit the footage, so I'm pointing it out.

I had the x3 and I have the x4 for 2 months now. DISAPPOINTMENT! It's not worth upgrading from the x3 at all. There are still many things that need to be fixed in the 360. For example, they should finally fix the point where the two hemispheres join so it doesn't distort. Also, the image still can't compare in quality to an action camera. And the 8k is also misleading since you'll get 4k on export. Just like with the x3, which was 4k but on export you got 1080. Overall, I would say I was very disappointed since I was expecting major upgrades and differences from the x3, but the differences are essentially negligible. Don't believe the vlogs you see that rave about how good and upgraded it is. Nonsense. That's how I got fooled too and sold the x3 to get almost the same camera. Since I got it, I used it twice and it's been in a drawer ever since.

*** For several months now I have had the x5. Same mess. What I have ultimately concluded after years with 360 cameras is that they are not worth as much as you think. Bad optics, not user-friendly at all, they distort in some areas, and they need editing before export. With all this, it's better to get a classic action camera or shoot your videos with your smartphone. You'll save money too. Watch most videos from bikes and such with 360 and you'll understand how bad these types of cameras are. ***

In all aspects, it is an excellent upgrade from the X3.
What impressed me is the dynamic range it has, where even in direct sunlight, the colors do not "burn".
It has incredible stabilization and any shot you take comes out buttery smooth.
A huge plus is that the package includes guard lenses that are easily removable, unlike the X3 where you have to stick them on.
It has very good wind cancellation on the microphone and the me mode is also convenient, where the camera automatically reframes on you and you have a ready video without needing to edit it in software.
Speaking of software, both the mobile application and the PC program are very user-friendly, even for beginners.
For the more advanced video enthusiasts, it has the ability to record in Flat mode so that you can do your own color correction in post-editing.
I believe that with an Invisible selfie stick to start with, you will be fully covered.
The only negative is that it heats up quite a bit, but without affecting the camera's functionality, especially if you constantly shoot in 8K. (the package also includes a thermal grip, so you're okay)
Overall, the camera does everything the X3 does but much better. Better resolution, colors, frame rates, helpful AI functions, etc.
So if you're thinking of upgrading, it's definitely worth it.