Buttkicker Gamer2, is it worth it?

Just clamp a big subwoofer to your chair. Same thing. All it does is use the subwoofer to give your chair some shake whenever a low sound occurs. In racing games it's the engine, same with flying game, but the guns and explosions also do it as well. What gives it the "big vibrations" is that it's mounted on the end of a short arm type assembly which amplified the low-end vibrations.

Given the price, you could probably rig up a similar setup for just over 1/2 what it goes for.