The pistol can be released from the CAA chassis in a matter of seconds, so it's not permanently attached.
And CAA offers a NFA stock option for them, even though the pistol is still "not" permanently attached.
CAA also has various generations with the EVO being the slimmest.
I don't consider the "fall away" stock set-up a PDW nor SMG as per the title of this thread, but the CAA chassis is in the same category as the other examples posted here.
It works fine for my Glocks and makes them more useable.
Variety is the spice of life.