Thanks, good stuff to think about!
As to what he'll use the light for, mainly he'll use it in his carpet cleaning business. Periodically he needs to check under furniture, look for spots in rooms with bad lighting, etc. So being easier to carry is a big advantage I'd think. Every once in a while he'll use the light for hiking at night - but he's really not a night person. He really only does foolish things like night hikes when he hangs around with his brother-in-law. (That guy is a flashaholic and a BAD influence on decent, hard-working, non-nocturnal people!

)
The grip and the throw on the Fenix seems very nice too. Hard choice.
He generally EDC's a multi-tool, so as long as the light isn't enormous, I don't much think it will be a problem for him to carry it.
I'd buy him a CR123A light, but he really doesn't like buying the batteries. He's just not an online shopper.