For a non-knife guy, I would look at the BK-17 with its traditional shape. I think the BK-2 or BK-10 or BK-7 is simply too large and he'd leave them at home.
I also really like the BK-24. Had it out for a run today. You will need some sort of handles on the BK-24 if he is ever going to use it hard. The sheath is the problem with the BK-24 as far as I'm concerned, but if he keeps it in a pack, won't really matter and the factory sheath will certainly keep it from cutting stuff inside the pack.