curious
I've never worn thigh bands, but I agree with @Angelina that driving with them just seems like a bad idea. When something dangerous happens and you need to speed up or slow down in a hurry, even a half second delay can be a big problem. If the chain or a lock gets tangled or stuck under your leg or caught on your dress, you have no time to fix it.
And if you do get into a bad accident, and there's any question about whose fault it is, and if it comes out that you were wearing thigh bands (maybe because you went to the hospital), I can't imagine it looking good for you in court.