The R.A.T 7 is actually very comfortable to use over long periods of time, which is nice considering that ergonomics and extreme customizability were key marketing points. This peripheral is one solid feeling mouse, as in, it has a metal frame instead of one constructed from cheap plastic. On the other hand, The R.A.T 7's solid construction makes it fairly heavy even with all of the additional weights removed. Keep that in mind if weight is of a concern to you. In any case, here are a couple of observations about the hardware that weren’t really stated in any of the reviews that I read. TL;DR: It’s a good mouse, I am very happy with it, though it may not suite your ergonomic needs. It's like a pair of pants, try it first if you can.
The buttons are fairly wide and seem to be designed for people who prefer to use three fingers to click (middle finger being on the scroll wheel). The width is perfect for me, since most other mice are too narrow to comfortable fit three fingers. If you don’t have sausage fingers or prefer to use a mouse with a standard two fingers grip, the R.A.T 7 is probably going to be uncomfortably wide. I also like the sniper button, though I wish it were located further back on the thumb piece so that I do not have to modify my grip to press it down. The profile switch buttons is angled in such a way that it makes it hard to see. I wish it also changed the LED colors of the sensitivity bar as well.
I really like the R.A.T 7’s scroll wheel: It is flat, wider than average, clicky, textured and loose. The scroll wheel was my primary point of contention with many of Logitech’s gaming mice: Some of the scroll wheels were either too “pointy”, way way too stiff or hard to press down without accidentally activating the side-scroll feature. The R.A.T 7 is absolutely perfect.
We will see how durable and finicky it is. In my experience, many issues don’t crop up until at least several months to a year of regular abuse. I’ve had issues with finicky laser mice in the past (which seemed to be related to an unclean mouse surface >_>). Performance wise, it’s smooth accurate and everything that I would expect from gaming caliber mouse.