The Master Ball is actually really useful if you're resetting for a 0 speed Pokemon. I can't imagine resetting for 0 speed Glastrier without using a Master Ball to make it happen; actually having to manually wear down and catch Calyrex the 50ish times it took would be pure torture.

That being said, when playing online, watch for what ball Glastrier comes out of. If it's a Master Ball, it's probably 0 speed. If it's not a Master Ball, either it's probably not 0 speed or it's just a hacked Glastrier (which, sadly, is pretty likely).