My view is that the Shock Isolated Millennium TurboHead and HA is more then enough reason to get the M4.
With the M4, you'll also be getting two Lamp Modules, and you can buy the N62 500Lu Lamp as an extra.
The Beauty of the 12PM [I don't have the M4 yet] is it's tiny size. For the amount and quality of light it produces, there is no better flashlight. Of course the downside is the runtime, but just how long will you need to have it on for? Seconds, maybe a minute at a time tops. Anything more, and you'd be better off with the M6 or 10X.
The M6 MN21 500Lu beam is bigger, brighter and even more impressive then the 12PM N62 Beam. However, I have the old 3" Extended Range TurboHead on my 12PM, and I prefer the tighter beam it projects at long range compared to the M6 MN21 "Flood" or "wall" of light.
I have the MN61 Lamp Module on order, and hope to have a review of all the Millennium TurboHead Lamp Modules currently available (and some that aren't
) in the near future.
The 12PM/M4 has a very important role - it's a specialist illumination tool, and more than justifies it's running costs. The M6 is bigger and brighter. Personally, I'd get the M6, but I have different requirements.
Al