There is one big shortcoming of the Touch Mouse: it only has one button at the front, rather than two. It detects which button you "intended" to press by seeing which finger is in contact with the mouse. (In this respect it repeats the very same mistake of the Apple Magic mouse.)
Two problems: firstly, you can't rest both fingers on the front when clicking, like you can with a normal mouse. I like to keep both fingers resting lightly on the mouse all the time, and then simply pressing a bit harder with either the forefinger or middle finger for a left or right click. With this mouse you have to lift the other finger right off the mouse before clicking. Some people do that anyway, but if you don't, you'll end up losing most of your right mouse-clicks (which are interpreted as left clicks if both fingers are on the mouse).
Secondly, you can't do any "chording" gestures with the buttons, such as are used in the Opera browser and, via add-ons, most other browsers. By way of example: a super-slick way of going back through your web pages is to hold down the right mouse button, and then click repeatedly on the left button - each click takes you back one page. Reverse the gesture for going forwards. After a few moments of practice, it's an incredibly natural, easy and fast way to navigate. Just the lack of this one feature means the Touch Mouse is a dead duck for me.
Actually, there's a third, smaller shortcoming. When you click the mouse the whole front of the mouse dips (rather than just the button like in a normal mouse). Again this is like the Apple Magic mouse. This feels really weird and wrong. You can get used to it, but it's unnatural. Your muscle memory expects just the bit you press to travel down and click, not the whole thing.
If Microsoft were to release a Touch mouse with two separate, moving buttons I'd buy one like a shot. Until they do, it's an absolute non-starter.
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