It has aux output which is the only way to input audio for many older cars. Your phone automatically connects via Bluetooth and you have a convenient display on the dash you can use to see what's playing and change the song. Not too many smartphones still have headphones jacks and having to connect your phone each time in the car with a USB to aux adapter cable is a little annoying. It also flexes all of the features Bluetooth audio supports (like album art) that even cars with Bluetooth don't always do. I almost bought one for my car but instead just cobbled together something using an FM modulator that was near useless in my area and a tape deck adapter. Works great and I have some basic playback controls in easy reach although a screen would have been nice. Buying an aftermarket stereo with Bluetooth would have been pretty expensive with the massive trim kit and the other crap I'd have to buy to keep my steering wheel controls working. I've also seen people using it on home stereos systems as well.

It's a perfect device to fill a specific niche for when you want Bluetooth audio but your existing audio system only has aux input or a tape deck.