I've had two RAT9s and another should be arriving in the post tomorrow or Wednesday.
First one the cursor/aim would suddenly flick off to the right. It made me run off cliffs more than once if I was running close to the edge and it suddenly turned me 90 degrees with no warning.
On the second the tracking was perfect, awesome mouse in every way EXCEPT one of the side buttons didn't click the same as the other. It wouldn't be an issue on a cheap mouse for but £80, I want a consistent mouse that isn't threatening to break.
I was one click away from ordering a mamba and a naga epic at different points, but a) they don't have the customisation options. b) The naga epic's button placement doesn't strike me as very wise (when I tried one, I'd move the mouse whenever I clicked one) and the mamba has less buttons. The biggest thing for me though was that if I'm going to spend £100 on a wireless mouse, I want it to be wireless. The RAT9 has that sorted with being able to swap battery packs. I couldn't find anything about spare battery packs/chargers with the other mice which means that if your battery runs out, you have to use it in wired mose, which defeats the point. If I wanted a wired mamba, I'd get a Deathadder for half the price.
Edit: If there's a problem with the new RAT when it shows up, I'll probably be going for the Mamba. It seems the better out of that or the naga epic.