It seems to have a fairly decent API and be pretty stable too which after having doing a wee bit of physics stuff myself, I can say is the #1 most important thing for any game physics engine. We did notice a couple of problems with the amount of friction in the demos seeming like they were a bit too low, but all in all it seems like its a fairly usable package. Seems like it might be worth checking out if you want some physics middleware but don't fancy the crazy prices of the big boys.