My buddy has an FM transmitter and it works great. We use it at work all of the time. They are not cheap though and are touchy. It has to be sitting in just the right spot to get a clean signal, or you get radio interference, so bouncing around in a car, to me, would be frustrating. The one he has has to sit motionless.

I'm sure the more expensive ones are good though, but I mean they are really pricey. The cheapest ones around here are like $50, for the lower end ones.

If you want to spend the extra buck, they are worth it.