I installed mine today- here is my experience. I had an older MM that I wanted to install it in but I discovered that it had been damaged by leaking alkalines so I bought 2 new MM's at Target this morning.
I measured 3/8" below the bottom of the crimps and cut there. The leads bottomed out before the crimps reached the plastic housing of the switch so I had to trim them a bit more. This is easy enough so I would recommend cutting them a bit long and using trial and error until it fits right. With the LED inserted so that the crimped flats touch the plastic, I installed my drilled reflector and tried it out. When the light first comes on it is at wide focus and it takes almost a full turn of the bezel to reach tightest focus. I could modify it a bit more so that it would be closest to optimum focus when it comes on but I'll save that for later. The beam was real good and smooth, the led appeared to be fairly well centered, no artifacts, nice color very close to white.
Remember I said I bought a pair of MM's this morning- so I put batteries in the remaining stock one for comparison purposes. Remember this is running both on the new Duracell alkalines that they came with. So here's the comparison... with both focused to their tightest point, the brightest parts of the spots appeared to be about the same. The stock MM is very yellow while the MJLED looks nice and white. The beam of the MM is very ugly- blotchy, oval shaped, has little holes in it, etc. The beam of the MJLED is very smooth.
The next step will be to get some lithium AA's to try with it.