XYZ Computing posted a review on the Kensington Digital FM Radio & FM Transmitter for iPod

The piece is also quite easy to use. It plugs into the iPod's universal connector doo-dad at the bottom and works from the second it's attached. Only a few buttons are present on the unit; one controls its transmitter role (in, out, off). A set of four buttons act as presets for those who are too lazy to tune the device themselves using the "+" and "-" buttons. Unfortunately, in order to listen to the radio, the headphones must be switched into the jack on the Transmitter itself. Not the biggest deal in the world, by any means, though.

Kensington Digital FM Radio & FM Transmitter for iPod Review