I just got my mako last saturday. It's my first mod. I think the big issue is that there's clearly too much variance in their machining process. On mine, the 14500 works without a battery spacer, however, I do have to leave one of the o-rings provided with the kit to make a solid seal.
It might also be that I am using it with a 510 adapter, which attached to the top piece differently, so it may protrude more into the battery casing. I'm not really sure.
Mine also works fine with 510 cartos.
I'll probably try and get a review up soon, as my experience has been a good deal more favorable, though I am less experienced.
Bill