I have a couple of Silent M590 and I'm quite happy. Scroll and center button is lasting a lot longer that my previous mouses (which is a welcome surprise), it's actually silent but with physical feedback (which is nice), and the shape and size are perfect for my need. So if I have to buy a new one, I'd probably go again for the M590 or I might try this M650 if it's the same price, as personally I couldn't care less about the colors and the "Unifying" vs "Logi Bolt" USB receiver.

@heffeque how's the battery life ? I mean how often do you change the battery with on average how much use a day ? The AA battery kinda puts me off.