Review on DAYKIT Mini USB Bluetooth 4.0 Dual Mode Adapter Dongle for Windows 10 8 7 Vista XP 32/64 Bit Linux - Improved Black Version by Stephen Zimmer

Do not buy more than one because all these keys have the same MAC address. This violates the Bluetooth specifications. You cannot use more than one of these keys in the same place without modification, since duplicate MAC addresses will cause conflicts. You can change the MAC address using a Windows program called Bluetooth MAC Address Changer or the Linux bdaddr command. Until you change the MAC address, these keys will conflict with each other and your Bluetooth network will not work. This is a common problem with generic Bluetooth dongles. Or, better yet, spend a few bucks more on a custom dongle that conforms to the correct Bluetooth specs.