Just picked this up yesterday, for use in my car with iPhone5. Car has a mini-jack input inside the armrest, to play (wired) devices through stereo, and while that had worked well for a few years, by keeping my ancient iPod wired inside the armrest, it was a huge pain to always open the armrest to change songs, etc.
I'm hopeful the product will provide trouble-free use for a long time (some of the reviews have me nervous about that...) But so far, so good.
I'm powering it directly off the car's aux power jack (also located inside the armrest) so I haven't had a chance or reason to test battery life. Only drawback I see so far, is tied to the very compact design (which I actually like, but...) The attached cord to connect the 3.5mm jack to the input is only about 2-3 inches long. In my armrest, the input jack is located at the bottom of a kind of deep storage well. The connection cord is not long enough to allow me to place the device up in the "top tray" of the armrest cavity. So I have to leave it down in the bottom of the well---which isn't a huge problem, except that every time I enter the car, I have to press the tiny button located on the device, to get it to connect to my iPhone. (It connects automatically and quickly each time I press the button, but you have to press the button each time -- apparently it doesn't sit there waiting to "auto sense" that my iPhone has come into range, each time I enter the car.) So I have to open the armrest & remove the top tray, to reach the bottom of the well and the device. Not the end of the world, since I do it when I first enter the car... But a longer 3.5mm cord would give added placement flexibility.
It is SO much nicer/easier controlling song selection from the iPhone5 (kept in my shirt pocket, or sitting on the passenger seat, or anywhere else handy.) Audio quality has been great - the Bluetooth transmission seems to provide a louder max volume level, too, than when I directly-wire the iPhone5 into that same aux jack, which is a nice perk.