hooray, I'm not the only left hander here lol.
from what I've seen, some left handed guns are a little more expensive. The only left handed gun I might get would be a bolt action. I also shoot left and right handed, keeps my game sharp on both sides. I've never been hit with any of my spent shells, while shooting left handed, so imo I don't think you have anything to worry about.
I don't have a Mossberg 500, I have a Maverick 88(literally the same gun, different furniture) never been even close the getting hit with a shell.
Speak softly and carry a big stick...just know how to use it.