The verdict is in: the Logitech RX300 mouse is out. The mouse-wheel buttons are too hard to click properly. The main mouse-wheel click, which replaces the traditional middle mouse button, is very hard to click because the wheel clicks twice: the first click happens when you press down with normal strength, but when you use your whole arm you can push the wheel further to get a second click, and this click is the one that actually works. The first click is just a decoy. This is annoying, but the problem is worse because it's very very easy to inadvertently tip the wheel to the left or right, thus activating the side clicks. This behaviour is annoying and it makes it difficult to manage tabs in Firefox: I middle-click to close a tab, but accidentally side-click, which scoots the active window somewhere else and closes THAT window. Or else I try to middle click something but realize I didn't lean on the mouse hard enough and only reached the decoy click.
It's too bad, because I like the rolling of the wheel better than my old mouse, but I depend on the ability to middle-click properly. Bye bye RX300.