I have a three-week old M6 LED in black, and a brand-new M6 LED in silver (probably from the first run, as it was the first shipment that BrightGuy got in stock). There are tiny differences in LED color -- the slightly older black one is a bit more white than the newer silver one, but it's only apparent if you compare them side-by-side. The beam pattern is also a bit different, but only because the first one has a virtually perfect circular hotspot -- seems to be sample-to-sample variation.
The switch on the new silver one is red, as was the first, but it seems to have a shorter throw. But the switch housing on the new one is a bit longer, so that might be the difference; the red rubber button doesn't stick out so far. It does make for a tighter fit in the belt pouch, esp. if you play with the focus a little. The focusing ability is still there, but there's not much difference from moving the head except to clarify the hotspot slightly, at least until you get a black center spot from moving it too far. I found that screwing the head down all the way wasn't the ideal setting, at least for in-house use at about 5-15' distances. A quarter-turn to a full turn off of the tightest setting did make the center spot smoother.
But if you adjust the focus, you might make the light long enough so that the belt pouch won't snap shut! The snaps on the flaps on each of the pouches I have seem to have been placed to fit the specific production run of each model, as they're not identical -- and there is no allowance for the longer length of the light with a focused head. The plastic or nylon spacer ring at the bottom of the pouch could be cut down, as it is very much oversized in length given the purpose of preventing the clickie from clicking, but it's beveled and smooth at the bottom, and it would be a real pain to sand it down to an equivalent level of finish to match the shipping condition!
I replaced both of the plastic lenses with UCL lenses from Flashlightlens.com. Worth the money, definitely. I also found it helpful to clean out the reflector with a compressed CO2 spray -- there was a surprisingly high amount of dust in there. The new lenses are thicker, so the bezel doesn't screw down quite so far.
The aluminized reflector is probably very fragile -- I was afraid to use the now-common gas dusters that contain potentially plastic-dissolving solvent gas, but the CO2 spray worked fine (I used a Craig rebranded, but no longer available, Innovations bike tire pump/inflator built for 12G CO2 cannisters with a long nozzle).
