I have an ICS:
-Barrel is standard. I put a prometheus TB in mine.
-Piston is still fine after approx. 10k rounds. As all the other internals.
-Exterior is really nice and solid. It went through rain, mud and sand just fine.
-Large battery compartment
-I don't have much experience with other mechbox, but this one is easy to open and modify (mostly V2 internals)
-Quick change spring!
-I didn't looked thoroughly but I can't find a better nozzle that fits...
-There's indeed no marking on the selector switch
-The original hopup bucking and sleeve on mine were not really good. Standard ones fit nicely and provide good seal.
On a side note:
-I'm not sure if the madbull DD rail is currently available. (If it is, show me where to get one!
) In the ad, they specified an ICS adapter for it also.
-Get a SA80 sling from UK surplus and search youtube for how to install it properly. It's a really nice sling system.
Hope it helps,
Fong