To give you an idea on how good these are… here I modded a Maratac copper AAA with this driver (gruppydriv rev.2 fw) and Nichia 219C.
Stock LED and driver:
Before vs After, In the photos the 1.6mm thick driver is shown, but I actually ended up using the 0.8mm one. Not necessary, but I added a solder blob top and a ring of soldering on the edge to improve ground contact. Minimal sanding was required to fit the new driver and it was secured with a couple drops of superglue.
This little FET driver paired with a low Vf LED allows much higher amps on a 10440 than with a XP-G2, according to my ceiling bounce tests it does about 750lm with a fresh efest 10440. Full build here: What did you mod today? - #634 by will34