The M3 is not going to be as bright as a G2Z with the high output P61 bulb. With the P61, the G2Z will be putting out 120 lumens. The G2Z using its standard P60 low output bulb will put out about 60 lumens. The M3 is capable of about 60 lumens, max. I know it is advertisd higher, but its bull. Even still, the Surefire beam, even with the 60 lumen P60 bulb, will be more perfect and without the imperfections you can see in the M3 light.
On top of this, I consistently hear reports of M3's not holding up. I read a lot of people saying they do too. All this means to me is that there's a lot of inconsistency in their product.
I dont know, I just think if you're going to do something, do it right. Otherwise why do it at all? No one is coming close to making anything as durable, modular or as useful as the Surefire.