I have one and it works okay but it's a pain for several reasons.
You have to find an empty channel on the band which isn't too
difficult, but if you are traveling any distance you eventually get
interference and then have to find another empty channel. then you
have to change the channel on the fm transmitter, which is a pain while
you're driving (and dangerous)...then if you turn off the car to run
into a store or something, when you turn it back on the transmitter is
back on the default channel and you have to turn it back to the desired
channel again..