I have the 2600mAh battery and matching door, and although I love it...it's not something that I would use day to day because of it's size.
This product sounds perfect for my needs. I'm not crying the blues over my 8310's battery life anyway (it's excellent!), but another 20-25% or so of juice on hand would be a good thing...especially since it fits w/o a special cover, so my Curve stays sexy and slim.