lots of guys in the western members section are running their trans. I myself have one of their stage 2 4l60e's and a yank 3600. no complaints.

 

Completely different transmission but the build a decent supra automatic.

 

For any trans claiming 5-pinion planetaries, I would ask for written confirmation they are ACDelco units and not aftermarket. While I don't have personal experience, I've had several trans builders tell me the current (Chinese made) aftermarket units are absolute crap and actually weaker than the ACDelco 4-pinion units.
Generally the website/ad will say ACDelco when they are, because it is an important feature. In that case, print out the ad and keep it; if the trans fails after warranty and the planetaries are not ACDelco, you will have a very strong case.
As always, just my opinion.