Infact I honestly can't come up with any "cons" to having one.
How 'bout this scenario....
We both have guns which use magazines. Mine doesn't have the mag disconnect.
Both of us lose, abuse, bend, fold, spindle or mutilate our magazine.
I can still shoot even if it's only one round at a time - you can't.
Which gun would you rather have in your holster when caught with your pants down and the feces just hit the air handler?
I'll take the one that still allows me to feed myself even if I don't have the luxury of multiple shots.
A pocket full of ammo isn't going to do much good if the gun doesn't go bang when you pull the trigger.
BTW - what's an "OSM" in english?