10 O'Clock cross-draw is pretty comfortable sitting, too. Unless you're "a big guy." But it's not for people with a conventional shooting stance. I shoot like it's a rifle even when it's not. 10 O'Clock, right-handed, body sideways, short arm, long arm, etc... Never any muzzle sweeping the room like someone going from cross-draw to a conventional stance. It also makes you a narrower target, since you're sideways. Well, for me anyway... I'm half the silhouette when I stand sideways as straight-on... I think it is all-around better. Cross-draw is also a form of retention. Plus, one skill set... It's just better.
I think it's dumb to learn two different ways of shooting. Especially when one of them is with a gun that is next to worthless (handguns). I'd rather OC a real gun, a rifle. Or a Mossberg Persuader. But the gun snobs here look down on that...
A shoulder rig is (usually) very similar to cross-draw. Be aware of your stance and how you get there... I think it's the best way if you think it through.