I am looking for a ball swivel fitting with 3/8" MNPT & FNPT for my 3/8" NPT setup (all couplers & hose ends are 3/8" NPT). I got a zilla whip hose but it had a inline swivel fitting not a ball swivel which IMHO doesn't do much since the air tool can spin in the coupler.
Something like the pic below
Something like the pic below
I have them on all my impacts (different brand but same design) and it's a noticeable power loss. If you're really worried about air flow just do a whip hose.