I always use it with extended mags. It's a little underpowered when silenced or at least I feel that way when I've used it silenced. The mind can be a powerful persuader. Regardless, it's very useful with extended mags. It doesn't really need an RDS because the iron sights are already really good. It's actually my preferred secondary.
Use it with a silencer on any class where my primary has a silencer. Extended mags on any class where I'm not using a silencer. Before the recent weapon buff it was better than some of the SMG's IMO. I trust it more at range over any SMG but the MP7.
It's a complete beast. Easily one of the best guns in the game overall. Almost no recoil, extraodinary range, even with a silencer and it has decent rate of fire.
I've ran it loud with EX mags and silenced. I prefer it silenced because of my play style, and I didn't notice any struggles still getting people from insane distances. With that being said, you'll kill a little quicker from distance with EX mags and won't have to stress as much when coming across multiple bad dudes.