I think it depends on where you live and the radio band usage in that location.
I live in the boonies, use an FM transmitter connected to my old 1st generation iPod touch, and rarely experience any interference at all.The sound while driving, with the road noise and whatnot, is close enough to that of the CD changer that I don't really notice. It'll do.
Things might be different if I moved down to, say, Tokyo, but for where I am it's fine.