"..I also received one of these today to drop into an Ultrafire WF-502B. "

Goodness me! You must tell me if that actually works at 400 lumens without melting your gloves. I too have a WF-502B with a couple of drop-ins and that drop-in sounds like a must have.

Sadly, about 1/4 of the stuff I have ordered from DX has been faulty lately. Eventually, I get a replacement but it takes forever.