I've been a ButtKicker user/lover/endorser for over 7 years, and I suppose it's easy for anyone who's not familiar with it to regard it as a gimmick. Also, they're not to be confused with any of the shakers and thumpers that have been out in the past, and were highly inefficient by comparison. ButtKicker is a pro-level, serious kicker.
I've always had it/them attached to the seat, never on the stand:
Yes, there are two
on there, but not because a single one is inefficient. On the contrary, one is plenty
for most drummers. But I've always kept two on two throne tops, because I run them hard and they have a thermal switch that shuts them down for 15-20 minutes if they overheat. It eventually dawned on me to just mount two on one seat, and simply switch over the cable when necessary. Then I figured out it was simpler still to bridge the two so they'd never overheat... and I've not had any issues since.
I send only the kick to the ButtKicker, with a gated signal so that other sounds like low end or snare hits don't thump me, run onto a crossover to focus the thump, and a Crown K2 amp, which has plenty of power for them.
I absolutely love mine.