KA13 is the updated version of KA3, so if you are already considering KA13, then there is no point of thinking about KA3. (note, that's how FiiO names updated models, so KA13 is upgraded from KA3, KA11 is upgraded from KA1, etc).

BTR3K is decent but it is designed as a Bluetooth adapter first and a USB dongle second. It will be a good choice if you need a device that can works as both, but otherwise I generally won't recommend it as a pure USB dongle because eventually the battery inside will degrade in a few years.