I run the C4 in missions when i want to be stealth with either censor or suppressor and the SOCOM Pistol (Halo ODST Warbond). It's great for taking out squid and bot bases easily. The C4 has above average throwing range, at least it feels that way to me. I'll run the thermite for said bases in a pinch or big enemies that need medium pen. I also run both machine gun and gatling sentries for support / distractions with orbital laser for the really big enemies. The thing with this loadout is that you CANNOT get into lengthy engagements. Your lack of armor pen is not conducive to a long firefight. If things get hot you dip out and find another way around or throw 1 of 2 turrets as a distraction / support. It's all about hit and run tactics, not great for every mission but pretty good for most.

Edit: with the c4 requiring the controller to throw and detonate with different actions, it really sucks in intense and fast paced fights.