I am very satisfied with this mouse. It is the perfect size to carry with me, the USB is stored next to the battery so it doesn't get lost, its weight is comfortable, and its use is very smooth.

I have bought 2 for myself (1 for the office, 1 for home), as well as another 2 for acquaintances. Incredible value for money, and especially the fact that you can adjust the middle button to side movements, is indescribably useful. Its only negative is that it does not have a Bluetooth connection and occupies a port (e.g. laptop).

I do not have much experience using this, it has not even been a month, but so far, it is what I was looking for and expecting. It is suitable for medium+ hands, good weight (takes 2 AA batteries - included) and enough buttons for extra functions beyond the 3 classics. My old Logitech (the 310) with one AA battery easily lasted over a year. It lasted a total of about 5 years. I hope it continues the company's good impression with the new one. Using it, I realized how much better a mouse that fills the hand is. This and the extra button functions make it excellent for its price.

I bought it since it came out.
The mouse is excellent, incredible battery life, no issues with the connection, excellent buttons and scroll wheel. I have cleaned it internally three times. After so many years, the external rubber where the fingers touch has worn out a bit. Heavy usage, at least 8 hours daily.
CAUTION: These comments refer to the M 510 wireless from the first ones released (purchased in 2010 or 2011, I don't remember well), the current ones are of different build quality and not as good.

Very good mouse. I have 2, one laser and one optical.
The optical one performs better on various surfaces.

Today, 26/4/2022, my wheel broke after about 6-7 years of daily heavy use. It feels amazing, like it becomes one with your palm. I went on skroutz to search for another mouse, up to 40€ at most, and even though this specific one has been on the market for quite a few years, I found it right in front of me and just ordered it again (32€) without a second thought. It works with 1 or 2 AA batteries, which last quite a while. I always have it with 2 batteries, and if I remember correctly, I have to change them around every year and a half.

For its price, it is simply impeccable. You decide its weight by how many batteries you will put in, while its size is very convenient for my hand. 6 months with one AA battery is not an exaggeration for this. Additionally, 2 buttons in a convenient spot. Wonderful mouse at a cheap price and durable. This is the third one I'm getting (the other two are still alive even though I managed to break the base for the batteries - is it possible to lose the final champion's league with triple the chances?).

Very good mouse for people with large palms, responds correctly to movements and clicks, I have had it for 6 months and the battery still holds, it was installed and recognized immediately by the computer without additional software, the only negative is that it is quite heavy compared to the Razer Mamba Wireless which is considerably lighter but they have the same size.

For now, everything is fine in terms of functionality and responsiveness, but the profile is quite high for me, which makes the wrist angle upwards when you hold it.
In the first few days, I felt my hand constantly gripping it, now in the third week, maybe I've gotten used to it somewhat?
Also, its sides are made of rubber supposedly for easier grip, but the material constantly feels dirty.
The wheel also gives you a sense of cheap construction from the first moment.
Perhaps these "drawbacks" are secondary for some, because functionally as a mouse, it doesn't currently have any issues.

(Photo for height comparison with a small lighter)

Finally, it's not a laser, but a regular optical mouse... I got it for 20 euros - it's relatively good for a mouse.
Weight - good, size - like regular desktop ones.

I don't change it, it's the 3rd one I'm getting, the first one fell down several times and eventually started acting crazy so I changed it, I lost the receiver of the second one and it cost almost the same as buying a new one.
It fits in my hand, the battery lasts a lot, and I don't see any difference compared to expensive models for gaming.

Excellent. User-friendly and clear, and at 40€ it doesn't have many competitors.
It is necessary to use it with LOGITECH software so that the additional buttons can be customized with any desired shortcut, and even per application.

From the best mice available in the market in my opinion, I have been using it since 2010. It is worth its money and it is a reliable choice for internet and gaming. The batteries last for months. The buttons are perfect. I bought a Corsair mouse for 90 euros last year and ended up going back to this one. Once you use a wireless mouse, you won't want cables on your desk again. I highly recommend it, it works flawlessly alongside the wireless keyboard from Logitech.

Very good mouse, I have it for 3 years and it hasn't shown any problems, even after so many falls.

I have it for almost 7 years and the plastic on the thumb wore off and almost all the matte surfaces got polished.
NO button has suffered anything, it works like the first day.
Batteries... you forget to put them in.
I use it for 4-5 hours a day, it's a workhorse

Excellent product! Very nice design and the battery life is unbeatable... I bought it in 2011 along with my laptop, and I remember only having to change the battery once! A very good choice, I recommend it!

The performance is excellent and the grip is very comfortable for my hand. So far, it hasn't presented any issues and I've had it for a year and a half. The battery hasn't needed to be replaced yet and overall, I am very satisfied. I bought it for 35 euros.

It constantly loses connection with the Receiver.
After a while, the cursor started "jumping" on the screen.

Far away!

+ Positive
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* The interface through `unify` receiver.
* The presence of side buttons that facilitate web browsing.
* Comfortable shape, "right" size for a desktop mouse.
* Low power consumption (I haven't changed the batteries for almost a year)

- Negative
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* The scroll wheel click stopped working properly after ~3 months.
* The `unify` receiver doesn't "see" other Logitech devices with `unify`, in my case the Logitech K360 keyboard.

Conclusion
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Satisfactory mouse for people who work with computers, probably not suitable for gamers as it lacks hardware capability to change dpi sensitivity.

Edit
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After about 1.5 years of use, it constantly loses connection with the receiver, which overheats and melts the plastic near the USB contacts.