Just purchased an authentic Surefire Helmet Light @ Fort Drum today to take overseas. Here are some pictures to show the differences btwn the real deal and the ACM clone.
Here you can see a few differences right off the bat. The Surefire light is a v.4 while the ACM clone is based off the v1 design. The surefire has a shield over the toggle switches to prevent accidental activation. As well it has an enhanced tailcap on the battery compartment with a "disable" feature. Useful for when you stow the light etc.
A rear view gives a better view of the shield and tailcap on the surefire vs the ACM. Speaking of the battery compartment, in the ACM version the compartment is a little small, meaning surefire batteries fit very snugly. As well it is slightly too long, resulting in the tailcap being a touch loose when closed and causing some flickering of the LEDS occasionally. No such problems w/ the Surefire model. Not a deal breaker my any means though.
Viewed from the front in darkness, this gives a pretty good indicator of the maximum illumination given from each light.
Ahh the moneyshot! Obviously the Surefire model blows away the ACM model in terms of lumens output.
Overall, the construction of the ACM model is a bit on the shabby side in comparison to the Surefire original. However for the low low price of $20US, it's a pretty good deal in my books. As most players will just buy one to attach to the side of there helmet, it will fill that role just fine. I'll be leaving my clone @ home however and taking my Surefire v4 with me overseas.