Some of you might've seen a thread pop up recently discussing a prototype of a set of headphones that essentially do the same thing (tactile or 'haptic' infrasound for <30hz. I can't find it so am assuming it got nuked by a mod for shillery.)
I met up with the lead engineer/designer on the project today to give 'em a test drive - no compensation/affiliation whatsoever, just me spouting off objectively like always - and I have some pretty strong impressions, mostly favorable.
Bear in mind they're still being designed... My overall first impression was extremely positive. The crossover handling translation into low-low-end freqs was very smooth and natural feeling, and the sound quality overall was excellent. More importantly it adds a really visceral dimension (as I imagine the subpac would) to one's perception of the mix. Although many of us try to notch out freqs that low to reduce rumble, if you don't know they're there or where they are it's kinda hard to do it without visualization... Unless you used these. You can also attentuate the level of vibration to match the [perceived] SPL.
The only somewhat noticeable drawback is in the slight latency introduced by the combo of motive driving and compensatory dampening in the mounting setup; there's an ever so slight delay in attack and a slightly more perceptible delay in release. Given that extreme sub bass always feels a little slower than high end stuff though this too doesn't stand out so much IMO.
If any of you are pro-hedz in the Bay Area (@cyclopian...) you should give him a shout and try 'em out. I think stuff like this has the potential to change music just by opening up new frequency ranges to explore.