I can understand this sentiment, as I always have a die hard 'OEM-or-nothing' attitude when it comes to serious tools. HOWEVER, I disagree in this instance.
FWIW, I have Surefire Kool-Aid administered intravenously, but I much prefer Gene Malkoff's drop-ins when it comes to LEDs.
Having EDC'd all of them at one time or another, in both a 6P and a G2Z, I've experienced no reliability issues with the P60L, M60 or M60L. The only difference I can discern is the better output, runtime, tint, and heat sinking of the Malkoff drop-ins.