i have the
TheraSpa 10 from brookstone. although it can work in the car, i don't use it in there. i have it on my computer chair, but i keep running over the power cord. it works ok, but nothing to rave about. it actually makes me feel itchy after a while i guess from all the shaking. i really prefer the massage chair because it feels like it's trying to work out the knots. this massage/heat pad is just shaking me up.
hopefully there is a brookstone near you so maybe you can chek one out before buying.