I'm also considering the buttkicker. Gamer 2 I believe. I used to have one before with my racing chair and it worked reasonably well. The only thing is, it's purely based on the audio output. Dosn't always match well with forces you would be feeling and limited.
The nice thing about applications like the ivibe TFS is, when the game supports it, you can model effects based on various parameters, like g-forces, acceleration, throttle-position and the like. For example, stowing landing gear can have a very noticable "jump" in your seat. Very immersive and love it.
Just doesn't seem there is anything else like that out there available for DCS.