I've got what's probably a dumb question. Without full auto capability, what is the draw of the 9mm "sub guns" like the Sig MPX or the Zenith Z-5? Don't get me wrong, they are way cool looking guns, and if money were no object I would have one, but what do they offer that, say, a Sig P226 doesn't other than a higher capacity mag? It seems that even if I were buying one to SBR it, I would still prefer something in 5.56.