I tried putting the XP-G2 in some of my old smooth reflector lights, as I like throw. The problem was that I was unable to focus it properly. Therefore the beam wasn't as smooth or as uniformed as I would like. This resulted in very small improvements. I ended up installing XR-E R2 in them, as they originally had Q5's.
I haven't tried with an OP reflector, so it may work well in your Nitecore D10? I have 3 x P3D's by Fenix and I am able to open two of them. The third one has an OP reflector and that is the only one I am unable to open. I spoke to David Chow at the time and he said that some of them can't be opened
The XP-G2 works really well in larger smooth reflector XP-G lights that are driven harder.