i had suomi - the worst smg ever. really tried to like it but it's just sucked so bad i had to get rid of it. same goes for ppsh-41. got rid of that one too.
kp m/45 on other hand i would SBR. by the way stan mags aren't great. reliability desired to be better. uzi are the best cheap smg mags right now. pps43 are great too if you could 9mm ones that is.