I have owned the original iTrip for the iPod, I own the second generation iTrip (with Digital Display), I have owned the Griffin RoadTrip with SmartScan, I have used the Belkin FM transmitter, I have used a Kensington FM transmitter, I own the Harman/Kardon Drive + Play (which is hard-wired to the stereo's antennae) . However, this recent incarnation of the iTrip is without doubt the best by a country mile. To say it is superb by comparison is an understatement.
I took it out today to London, where every other FM transmitter has failed due to severe interference, but this iTrip handled it effortlessly. Also, the SmartScan is the best in relative comparison to any other Griffin iTrip.
I cannot recommend this iTrip enough. Also, for those people wishing to use it with an iPhone or iTouch can download the superb app from Apple Store for tuning etc.
Don't expect this to perform as well as an aux input, but for an FM transmitter in my honest opinion this is the best.