Below are the pictures of the Billionton Bluetooth Class 2 USB dongle that comes in blue clear plastic casing. I used these dongles in a few projects which require an unexpensive UART bluetooth module. It can be found for approx. $15 here in the USA (Ebay is your friend). The only catch is to get the right revision (pictured on the left), see below...



On the left side there's an old revision which utilized CSR BC2MOD2C module with BlueCore2-External and 4Mbit of flash memory. Some of them may have an old HCI 14.7 firmware, newer batches come loaded with HCI 16.14 firmware which is the latest known release available for 4Mbit BC2-Ext. This dongle can easily be switched from USB to UART mode with re-programming appropriate parameters stored in the persistent store. The dongle uses balun and has an electromagnetic shield over BT module (you can see the metal shield thru plastic casing).

On the right side there's a newer revision. Little is known about it besides that it's claimed to be BT spec 1.2 compliant. It might even be using BC3, and it may not be possible to switch it to UART mode. It doesn't have an electromagnetic shield. Unless proven otherwise, stay away from it!