itrip is obviously a good idea, however it fails to meet the standard on a number of points.
1 - the range. it's range is certainly not impressive, despite it working /okay/ in the car. about 1-3m range from a stereo, sometimes fuzzy in car. very average.
2 - audio quality. has noticeably less than a wired solution.. which is an okay trade off, but it means that if you have a car kit tape player, you'll probably end up using that again
3 - tuning method. uses a series of mp3 files to tune. if you don't remove these files after you select a frequency, it's very possible to accidentally de-tune during random play. on top of that, my itrip is frustratingly creative about what frequency it chooses, despite which one you indicate.
4 - interference. becomes a point if you remove the tuning files. becomes an issue especially when traveling.
5 - no access to hold switch while itrip is plugged in.
6 - and now after all these shortcomings, my itrip has stopped working, leading to this review.

i'm not sure about the competing products, but this sure it's the holy grail of fm transmitters.