Malkoff dropin is so much better than anything I can think of.
Everything about it. Easy to fit and swap to other light.
XPG dropin is $39. I reckon heatsink is worth $30 on it's own. It is 2 part, with a small angled piece that tightens with a screw to secure in Mag tube.
Provides good contact for heat transfer, allows some height adjustment of dropin for using different reflectors.
The chance of this dropin outlasting anything else you buy is extremely high.
It will maintain high output continuously with no risk of anything overheating.
Good beam with stock mag reflector. I use with FM deep or 2.5 Throwmaster reflectors and turns it into awesome thrower (with very low power)
With 6 NiMh cells it will draw about 0.5 Amp so long runtime.
I have both XPG and XML Malkoff dropins. Both excellent. Big price difference between 2 dropins, while I think XML is good value, XPG dropin is excellent value.