Just don't like it's strange design, expensive price, even battery life is quite long.
Well, the "Strange design" is the point of the mouse, and is really a personal preference thing. For those of us who like chunky, sculpted mice that you can really rest your palm on, there really isn't a lot of choice on the market at the moment unless you go for gaming mice (which tend not to be wireless) - most mice seem to be heading down the portable/low-profile route.
(Any left-handed people can forget it, of course - thank you for not shooting the messenger on the way out)
Heck, some people actually seem to like the Apple Magic Mouse - personally using one of those makes me want to gnaw off my hand.
I've just got a MX Master - but previously I've use the MX Performance which is a very similar shape. I'd say the MX Master feels very slightly nicer in the hand, but there's not much in it. If you like this shape, you won't want to go back to anything else.
Not sure how much use I'll make of the extra buttons - I didn't use them much on the MX Performance. The horizontal scroll thumbwheel seems promising, although the back/next buttons have become rather fiddly as a result. The 'gesture button' on the thumbrest is an interesting idea: hold this down and swipe left/right to switch desktops, up for Mission Control etc. (all reconfigurable) Time will tell if its useful.
Like the Performance, the vertical scroll wheel is quite heavy and will stay spinning for a while if you give it a flick, there's a toggle button to give it a 'click wheel' action. Unlike the Performance, the toggle button is now soft and the click wheel action engages electrically. Move the wheel slowly and it 'clicks' - give it a flick and it spins freely for rapid scrolling - again, time will tell if this is brilliant or just something to go wrong. If you always have it in this mode, you can re-define the toggle button: I've got it toggling between two sensitivity settings.
Other neat features: the USB charging cable is designed so that you can still use the mouse while it is on charge. You can pair it with up to 3 different receivers (Bluetooth LE or Logitech dongles) and easily switch by pressing a button underneath.
