I bought a Multiset of Q2's for my son and I to use primarily for bike to bike and it works wonderfully. I also have a 2820 GPS with Bluetooth and my phone syncs to it and it syncs to my Q2, so I can talk bike to bike, receive and make phone calls thru my 2820 and listen to turn instructions from the 2820. If you don't have a Bluetooth GPS, you can link your phone directly to the Q2.
The FM receiver has limited range, but I have found a valuable use for it. My Sirius sat radio has a built in FM transmitter, so I set the Q2 to receive the broadcast of the Sirius and can listen to the radio.
The Q2 has a built in MP3 jack, but I have found that volume output from it is not sufficient. Others have used a FM transmitter on their MP3 players and I would think that is the best way to listen to MP3's. My 2820 has a built in MP3 player and I can listen via Bluetooth, but I prefer to listen to the Sirius radio instead.
We bought these over a year ago and have used them on several week long trips. They usually last all day, about 8 hours. On a trip this past October mine started to go dead after about 4 to 5 hours. I contacted Cardo customer service and they replaced it with a new unit.