I used to have one, and it was pretty good (for an FM transmitter). Depends on your location as to how easy it is to find a clear frequency to broadcast on, and if you drive long distances you might need to retune
I've read these are pretty good, but I got a Kensington RDS transmitter and I thin it works well and charges the ipod. Scrolls track & artist name on radio display which is quite cool, and sounds reasonable IMO the same as an actual radio station, with very little hiss. We use it for trips to the highlands to visit family and finding a clear frequency is a doddle. (I find 107.9 works well around most of Glasgow) Managed to get a used one off ebay for around half the retail price.
I find the Macally Fm cup Transmitter OK but did need to retune several times driving from Dover to Leeds. The design is good in that it charges your ipod and it fits arm rest box when not in use. I have a 2nd Generation ipod Nano and it just clear of my arm when changing gear, the 3rd gen Nano is not as high so it should be better. Honda should have designed the radio unit to incorporate ipods.