I don't usually use SMGs but I actually got that thing gold in a little under three hours when they released it for Season Pass holders a few weeks back. I wasn't even really trying and only finished it up when I saw all I needed was lean kills.
I typically run Suppressor with Grip or Extendo Mags. I used it in the Onslaught Deathmatch playlist and it worked out really well on every one of those maps. Oddly, I found it more suited for those maps than the Maverick which released with that pack. I can only assume that playlist is gone since Devastation is up now. I would assume it should work fine as all the new maps seem to be about the same size as the Onslaught ones.
The key is to know when to switch to the AR and back. I typically ran around in SMG mode but when I would ADS and see a dude at medium to long range, I would switch it up and us it in AR mode. With the AR mode, accuracy is key as the fire rate slows. As an SMG, it fires so fast that you can hipfire people to death even without steady aim which is its biggest draw. That fire rate is insane. With Grip, what little bounce it had is pretty much completely gone.
It's an awesome, versatile gun unlike the Maverick which I though was a little underwhelming. The only real down side is that the reload is brutal. SoH is your friend. I also found some success with Marathon and On the Go and just never stopped moving.
"Cover your receptors Perceptor." Driver picks the music. Shotgun shuts his cakehole.