USB Bluetooth 4.0 Dongle that works without proprietary firmware
If you’re looking for a USB 4.0 Class 1 Bluetooth dongle that has Linux compatibility without needing proprietary firmware, the BT0015 by LogiLink is one option that works. I personally tested it with Trisquel Linux and Gentoo Linux without additional firmware, and can confirm that I’m able to use it.
Since LogiLink sells multiple Bluetooth dongles, make sure that you buy the one with the article number “BT0015”, just to be sure you get the right one for your liberated Linux distro of choice.