When you install the Logitech SetPoint software (not included in the OEM package, but available from the Logitech site), you can remap the two smaller buttons, so that it receives the function of a third mouse button. The software also displays the charge status of the two inlaid AAA batteries.
I have to use only relatively short while, but it seems to me this mouse to be a real value-for-Tip.
PS: when I bought the mouse, it cost a little more than 20 euros.