You can see that almost any device will work, but you should get one from the confirmed working devices, just to be safe. There's no real benefit for buying a more expensive one, even the cheapest ones will do.
I'd recommend a Samsung one. I bought non-samsung and after 30 days the trial of their BT stack expired. I searched and tried clearing my entire registry but the expiration still remains. In order to pair a Wiimote with motion plus you HAVE to use the Samsung BT stack if you're using this with Dolphin.