Two stage triggers are indeed handy in the 38. Since the 50's and Hispanos fly fairly similar, you waste less cannon rounds by ranging with the 50's first. You'll run out of cannon way before you run out of 50's if you don't have them mapped separately. That's not a death sentence, but no cannon means you're not nearly as lethal as you were on takeoff.
If you're snatching the trigger, you're pulling a Cougar and holding on too tight. Heed the words of Sam Snead and pretend it's a baby bird. Keep it from flying away, but don't kill it. That said, I've found it useful to map cannons to a separate thumb button too, but I pretty much only use it in the K4. I like shooting taters by themselves and save my MG's for backup duty or plinking a runner. They're pretty much useless otherwise.