I do have one issues though. I don't feel like my M20 is as bright as it should be. I have the Jetbeam M1x, which is rated 400 Lumens out the front and it completely blows the M20 away. I compared it with the Surefire U2, which is rated for 100 lumens, and the M20 is only a tad brighter. I've tried running it on 1x18650, 2xCR123, 2xRCR123 and it doesn't make a difference. To me, it seems like the M20 is more in the 200ish lumens than 500. Did you guys feel the same way? Did I get a bad batch or is my eyes just going bad?
There is one thing wrong with you comparison, the M1X is a thrower (I do not know about the SF), it will always be brighter than other lights with same or even higher lumen rating. If you have a small room with white ceiling and walls, try shining the lights at the ceiling and look at the floor, this gives a much better comparison of lumen (But is not perfect).
If you look back in this thread you will see my take on the light output of the M20 Ti and if you look here you will see how it looks compares to some other lights.