The Kriss Vector really shines when used as a select fire subgun - and even better when it's suppressed. It makes for an interesting pistol too, however. Ask Garand Thumb how he knows.
CMMG's Banshee runs off of standard Glock 21 mags. They're solid mags, but limit capacity. Kriss's MagEx extenders offer a great solution. Here's how they work.