I've also got one. A fair few wires involved hanging around the dash, but if it's that or nothing then go for it. The FM transmitter thing works well and there's a function for automatically finding new empty airspace when you start picking up other stations.
Very good though – didn't drop any signal the whole length of the M4, and I could listen to test match cricket all the way home, or even just R5 with good quality signal (which is quite refreshing in fact).
I hate the wires though, so in the new car I'm going to wire a 12v socket and the related wires into the centre console storage box and leave it in there, using the preset buttons to change station if I need it.
It's also worth noting that you have to leave the aerial stuck on the window, so thieves will always know you've got one.
I'd seriously consider getting a head unit with it built in tho.