Stuns are by far the most inconsistent iteration of stun nades I've ever played with in any videogame.
They are completely hit or miss. The only thing I'm confident that they will do for me is use up the 2 ADS nade maximum when I need to get rid of those. I actually saved a clip from last night where I flash bang a door seal where buddy is staring at, run in the room, only to get bodied by a shotty. I watch the kill cam, and I see him LOOKING right into where the flashbang goes off and not effect him, cause he killed me right when I stepped in the room, and he wasn't just spraying like crazy.