I'm using it on a Droid2. I just got it about 2 hours ago. I had some trouble pairing it. I wasn't sure if it was charged or not, due to the lack of a "charging" light. I tried with my phone (droid2) and the gf's phone (S5 I think), couldn't get it to pair. I flipped the switch on the back to off and back to "A" (Android), immediately searched for Bluetooth devices and I was able to pair it.
The buttons could be bigger or bubble-like for my caveman fingers to feel what I'm pushing in the dark while driving.
This will make my less distracting while swerving around the cars with the yellow license plates in the left lane with the high beams on while my phone is doing that awesome droid-blinking thing when you look at the audio cable wrong.
Waterproof would be a nice addition to this product, so I can control my phone from the shower/pool, or while getting all sweaty doing yard-work