Must not be a Mac mouse. More than one button just lacks Mac's simple elegance
Which is a alternative way of saying limited capability.
Or making easy things more complex in the case of a single button mouse and then having to use the keyboard and second hand to perform a simple right click. Apple's 'simple' is all too often actually simplistic.
A mouse that disguises the fact that is in fact a multi-button mouse is no different from an actual multi button mouse and is just Apple's way of avoiding losing face by admitting that a single button mouse was in fact a really dumb idea.
Another example of this 'elegant simplicity' is the omission of cursor keys in iOS with the solution to their absence being far more complex, fiddly, slower and at times downright infuriating and difficult to use. Job's obsession with getting rid of buttons had him even try remove cursor keys from physical keyboards too, but thankfully he was dissuaded of that particularly dopey idea.
Thank god Jobs never designed cameras, as they would only have a single button for the shutter and all other controls would be buried in menus as adjustment dials and ergonomic buttons would make it less smooth. Not to mention you'd only get the choice of one form factor, one sensor size and one focal length because Apple would know better than you what to use for all possible scenarios.