I have the Buttkicker Gamer... probably not as good but still it adds a lot to immersion and any game supports it by default. It's driven by LFE frequencies from your sound card.
It's particularly cool in BoS, I can feel the ground on taxiing, turbulence when flying through clouds, and of course gunfire from my own guns and when my plane is hit.
In CloD, I even feel the stress on the airframe at high G's!
I'm sure GameTrix is much better, but Buttkicker is cheaper, easily available and damn good!
(No, I'm not a sales rep, just a happy customer who wishes he had gotten this long ago!)