I just got mine - fit and finish is great, and the Surefire X300U is a perfect pairing with the MK23. I've had other adapters before, but finally, the light is as close and snug with the frame and trigger guard as it should be. (And it just barely fits, with the light, in my LB drop-leg holster - woohoo!) I'll have to take some pics of the setup within the next few days.
Huge thanks to @gator33 and @Sextus - it is highly appreciated!!!