Already, I love the ergonomics of this model. I do not have very large hands, for a man, but I appreciate the rather large mouse, which support well the palm, and it is the case of the MX Performance. It is relatively heavy for a mouse, but it suits me very well. The glide is very good, and the "dark field" sensor is very effective: no need mouse pads, even on the office boardroom table: it is the only work on this table.
It also has enough extra buttons for my use: middle button (wheel), wheel that tilts to the right and left, previous and next buttons, button "zoom" button and "change application". Knowing that these buttons are configurable via the Logitech SetPoint driver, it leaves something to concoct ergonomics with onions. Especially it is possible to customize them for a particular application (1 Profile for Excel, another for Sketchup, a third for ...). Very convenient.
The mouse sensitivity is also adjustable, but I have not yet had the usefulness of this feature (I do not even know if I will have one day).
Concerning autonomy, it is very correct: 1 week of intense use (10-12h / d) before the charge level signal. but what's interesting with this model is that you can continue to use it even when it is charging as there is no support but a USB cable. See you then almost with a wired mouse. Almost, because you still have the unifying dongle is plugged in, and the microUSB cable is too rigid to be really nice (I've also replaced by a longer and more flexible).
In short, it is a mouse that has the benefits of wireless without the disadvantages that blocked me before.
The battery is a 2000mAh NiMH standard AA-size (LR6), and its housing allows to slip the dongle unifying for transport: 2 very good ideas.