I have been really happy using it, but it's fairly large, so if you have medium or large hands it should work fine, but if you have small hands then I wouldn't recommend. It is really good for keeping the precision of a regular mouse - which people say is hard to achieve with a trackball unless you sacrifice speed.
The top button allows some gestures, and what they do you need to configure, say you hold top button and swipe right, this could be like alt+tab, switch workspace, or whatever you want. Logitech has a little (Windows only) Software where you can configure it. There's an open source version people made for Linux of that software. I don't know if there's anything on MacOS - from either logitech or the community.
This one also has back and forward buttons on the thumb side, they are alright.
I had a lot of wrist pains that are gone after using this mouse - I use it for work and everything. In my country I have seven days to return anything I buy online for no cost, so I just bought and experimented with it.
The only thing I dislike in the mouse is the wheel, for the price of the mouse I expected it to have the wheel that other Logitech mouses at it's price point have and it doesn't, it has the wheel of the cheapest Logitech mouses. The other Logitech mouses have inertia...