I have a Surefire G2 on a mount from CAA and a pressure switch from TacStar. Whole deal was about $100 from Brownells. Some people don't like the TacStar switch as it eventaully breaks, but at $20-30 I can get a whole box for the price of the same Surefire part ($130). Would I take it to the sand box? Probably, with some spares. Haven't had a chance to really beat it to death but it has held up well so far.
If he's Cav Scout he'll be in and out of vehicles a lot, so anything that hangs up will be BAD. The remote switch's cord can be run under the handguard to get it out of the way. If he's got the quad rail M4, Falcon (ErgoGrip) makes a rail cover that holds a remote switch better than just the tape they come with. Old bicycle inner tubes cut into small strips work good too if it's on a foregrip.
I have, and will probably remove, a verticle foregrip. I tend to hold the mag well and mag instead, even with the grip in place. Makes mag changes a little faster too. Some people swear by them though.
Tell him to stay safe and best wishes from here.