So I ordered this accessory after some research since pretty much the only place I need hands free is in the car. It's a big speaker that clips to the sun visor and also transmits on an FM frequency. I got it because I'd be able to play music through the car stereo this way, which is great because the CD player in my dash is not that great.
So I set it up and the FM reception is not that great. One interesting thing is that shortly after I got it, Pandora released an update that allowed it to be played over Bluetooth.
The FM reception essentially only works if I leave the charger cable plugged in. What I do is, I have the official Motorola car charger for my DROID X and I just keep it plugged into the sunvisor speaker. I just charge my DROID at work on the USB cable to my laptop.
The call quality is fine, not great, not terrible. About what you'd expect for a microphone that's like a foot away from your face. I don't use the speaker much, it's always in FM mode, but the quality there is fine.
Finding an FM frequency is kind of a pain. I think it's supposed to be able to go up or down but I think one of the buttons on mine doesn't work. So it can only go up. The frequency is adjustable in tenths of a MHz but my radio can only tune to the odd tenths, which is interesting. Also I thought it would be better to find a frequency with no station on it, but the reception almost seems better when there is already a station on that frequency.
Start up is a pain. Whenever I get in the car there is static on the radio until I turn on the visor unit, wait until it connects, then press the FM button. I wish there was a way for it to automatically reboot in FM mode already.
What I want to do eventually is get one of those car lighter things with multiple USB slots in it so I can just use regular Micro USB cables to charge both accessories. Speaking of which, I think I'll see if I can find such things. I've only seen ones with two USB slots but it would be cool to have like, four, so a passenger can charge their stuff, too.