This unit holds much promise. It is neatly self-contained and has a headphone socket, USB socket, SD card socket, as well as bluetooth. It also has two different remote controls.
It's very easy to set up and use. It seems to put out a reasonably strong FM signal - other similar devices I've had have been so weedy that when listening on the radio you'd get lots of bleed-through from (weak) broadcast radio stations. So far, I've encountered little of that.
As far as I can tell, the phone call functionality works well: I accidentally called someone while fiddling with the buttons, and I could hear them clearly in the car.
My big disappointment was that I wanted to be able to stream music and sat nav guidance from my smartphone to this device via bluetooth, and I can't make it happen. There are two relevant bluetooth profiles - one for a phone headset, the other ('A2DP') for streaming audio media. The (rather brief) instruction manual for this device says it does the latter, but I can only make it do the former. I've tried pairing it with two different Android devices, with different Android versions. In the advanced settings for the paired device, you'd expect to see a tickbox for streaming audio ... and it's not there :(.
The product description on Amazon doesn't promise A2DP; I just read too much into it. Hence my disappointment.