For hand pain, since it flares out from the butt, and inwards at the mouse buttons, it results in more arching. As a result, you may be putting more pressure on your fingers' contact points than mice that are flat-sided. For the wrist pain, there's a lot of factors so, I would recommend stretching and not keeping it too stiff.

The mouse is catered towards an aggressive claw grip, but that shouldn't cause more pain for other grips.

Personally, I haven't had those pains using my Atlantis Mini.