I recently bought a Bluetooth 4.0 USB adapter from BlueRigger, because I wanted to use a wireless headset on my desktop computer at home, and it doesn’t have Bluetooth built in. It didn’t quite work… I was able to listen to music just fine on my headset, but when I tried to switch it into telephony mode (i.e., activate the microphone), it stopped working.
I emailed BlueRigger about the problem. They worked with me aggressively to find a solution to the problem. Eventually, they concluded that the Bluetooth 4.0 adapter, which has a relatively new chipset in it, is incompatible with Linux, but an older version of the same product is fully Linux-compatible. So they sent me one for free, and indeed it fixed the problem.
Well done, BlueRigger.