To tell you the truth, the only reason I'd get a KL2 would be to see what I could fit in there. I wouldn't even consider running it in stock form. The M3 is just too big for the amount of light that the KL2 puts out. The KL1 and KL3 are also more technologically advance with regard to regualtion, etc. My KL1 puts out alot more light than a KL2 does.
I guess I'm saying that I just wouldn't buy an M3 for the purpose of putting a KL2 on it. That's alot of money to put into a light that can't compete with less expensive lights in the LED arena.
BTW, if anyone has come up with a cool KL2 mod, please speak up. I'm really interested in something with a 5W and a reflector with regulation.