I consider them machine pistols due to size, despite having a bolt instead of a slide. MAC 11s and Skorpions have belt holsters available, complete with mag and silencer pouches built in, both have stubby carry mags available. The Skorpion is always called a MP insted of SMG, the little MAC too. More compact than a HK Mark 23. I believe the VP-70 cannot rock n' roll without the detachable stock in place.
These blur the line, seem more of the pistol type though with cyclic rates and such. Both their stocks (Mac and Skorpion) are a joke.
The Jatimatic has no way to attach a stock (and can reportedly be controlled one handed on auto) but is probably bigger than MP5-K. Maybe those 2 and others like them such as the KG-9 auto, or the chopped and channeled Swedish K's of Vietnam, are just subs or PDWs without a stock...they fit any category but are too big to be called MPs, stock or no stock.
The first subguns, the huge, wood stocked, carbine sized tubers, were termed machine pistol, before and a little after the term submachinegun was coined for the TSMG. According to the designer for HK, the full MP-5A2 is one.
Machine pistols generally have a notorious and unsavory rep. They are usually not tactically sound choices for LE, SD, or Military use for most any application, to the point a regular pistol would be prefered. It takes a lot of training and practice to handle proficiently. Some anti-piracy ship security teams use Glock 18s, and the Stechkin gets a lot of play in Russian gangbusting. Otherwise, just a concealable ambush buster which found their niche with revolutionaries, traffickers, hit squads, hijackers and desperadoes. Not to say it's inherently evil, just that for the most part they fit the BG gun stereotype.
I think they would be fun as hell to play with. Shot a Spectre SMG long ago (stock folded over), could have done that all day