This is a top-end FM transmitter that should appeal to anyone who wants to broadcast their iPod to a car radio. The key things to look for in an FM transmitter are signal strength, sound quality and ease of tuning. A decent signal strength is especially needed in urban areas where your transmitter may have to fight off local stations as you drive around.
The Kensington RDS FM has excellent signal strength and came through loud and clear for us while driving around. Big tuning buttons and a clear display are also things to look for, for obvious safety reasons. Again, this one scores well; it uses the iPod's screen to show you the frequency it's tuned to - no transmitter with a built-in screen will have one so big.
It also has a simple two-click metal panel for tuning your channels. One tuning niggle is that this transmitter only moves along the dial in increments of 0.2MHz, so the progression is 88.1, 88.3, 88.5 and so on. If it moved along in smaller increments of 0.1MHz it could tune more precisely.
As a bonus there's a unique feature available here. Kensington's transmitter has the ability to broadcast an RDS signature along with the music. This means the name of the track and artist appears on RDS compatible radios as it plays. We tested it and found it works with both files you have named for yourself in iTunes or bought with tags of their own.
The price is towards the top end of the scale, but it does include a charger cable that not all transmitters come with. Some transmitters have weak signal strengths and sound quality does vary, but the Kensington RDS FM is a good all round performer and it's definitely worth the money.