I have one of the first generation models, before they got all tactical looking. I just use oem 10 round mags in mine. There are apparently higher capacity mags out there but I've never tried any.
I mounted a scope on mine when I first got it but quickly realized a scope on a 9mm carbine was total overkill, and took it off. A red dot would probably be nice but the iron sights work just fine, for what it is.
It is a fun, cheap plinker. I like banging away at steel plates with mine. People turn up their noses at it until they actually shoot it.
