I have both the MBR-100 and the BB remote stereo gateway. The MBR-100 has good sound quality for bluetooth, but to my ears the BB sounds better. The MBR-100 has to be charged about every 5 hours (with a proprietary Sony Ericsson charger), while the BB does not have a battery and needs a mini USB power connection. The only problem I've had with the MBR-100 is that I have to reconnect it after taking a call.
Having to charge the MBR-100 is why I use it around the house (put the droid on a shelf and out of harms way, with my ear buds connected to the MBR-100 in my pocket) and not in the car since I always forget to charge stuff in my car. I have the BB in the ash tray of my car and it's wired for power and aux behind the dash. No worries about running out of juice and after I turn it on I close the ash tray and stream pandora without a wire to be seen.