I have a Sound Performance Gen-II tranny (if I remember right), not the most expensive, basically an upgraded standard box.
Hand on heart I can only say I got a .05 second improvement after fitting the box, maybe something else changed, maybe it was the weather (and continues to be!).
The old box already changed sweetly, smoothly and quickly, the new one is much the same but if I switch the switch that increases the line pressure, it gives more of a clunk.
Listen to the change of an auto Supra with a stock box; it really is quick.
They probably are but it is not really reflected in my times.
I had not used them before getting the new tranny. They reduced my time by .5 seconds. (BFG)
I may be wrong but I think whoever you get it from you'll end up with a PI one (in pink! OK, lilac, lavender or some colour like that).
Mine (actually my wife's) is a UK spec so already has a cooler, but we are thinking of changing to the Fluidyne plus a fan.
If buying a TC or box again I'd probably use Vortex. They were just starting up when I ordered mine directly from the US. They're such helpful guys.