: Did they actually work in single player? If so did having two stacked on top
: of each other improve their function, and did having a super shield
: stacked on top of that negate their effect?
It looks like they don't, and they don't seem to function like the ones in Doom either (i.e. you may be seen but enemies can't aim well at you), but I think that's because you need to be in a dark room.
For example, the shadow chip/transparency/active camouflage on Try Again is a must for Ingue Ferroque as the fighters and troopers won't see you in the dark round areas at the start while it's active and they only start moving when you fire at them. However, try it on the hunters and/or enforcers in Try Again instead and it never fools them.
I was too used to Active Camo in Halo 1+2 as well as unrelated games with actual invisibility so both Marathon and Doom's ones caught me out when I first used them.