^I think the original concept of the Suomi was along the lines of the TSMG, sort of a cross between SMG and a short range light machine gun. The Beretta 38 SMG's were along these lines too, and allegedly, were highly sought after by German troops in WWII; you can take that for what' it's worth. The Suomi served the Finns well, if you read up on Simo Hayha's (spelling) account of using them in battle. :D
Edit: according to Gunwriters on the Web, the Suomi was used to provide covering fire in some battles, you see it had a quick change barrel feature along the lines of an MG-42. Incredible foresight on Mr. Lahti's part.