First I was using the Naos 8200 mouse and got excruciating hand pain which only got worse and worse with time. When I realised that my hands are not going to get used to it, I exchanged Naos for an Avior 7000, and that model, while much better, is not comfortable either. The problem is bad enough that I'm now buying another mouse of a different brand.
I don't know, maybe the fault is with me, but I have to say that I have an average-sized hand and that I never had a problem with ergonomics of any mouse before. I used Logitech MX Revolution, Razer Abyssus and several cheaper mice in the past without any problems.
I give it two stars because apart from this, the mouse seems solid with lots of options for customisation. In fact I'd say it has too many - who on earth wants constant blinking lights on their mouse? Instead of devising such useless features, I suggest working on ergonomics, Mionix!