Interesting, never looked into finnish flamethrowers, but looks like they wanted to do the soviet thing- make a flamethrower look like other wepon from a distance for operator safety.
Or is it a crazy underbarrel addition to the Suomi SMG?
Its underbarrel attachment, the SMG is functional.
It was supposed to be for trench and bunker clearing,
They tested it and dropped it.

This is "korsu" variant(bunker)
It has no front sight and the barrel is tapered, IN ORDER for a person inside a bunker to be able to shove the barrel through very small portholes and engage enemy at close quarters.
The shroud is longer than the barrel, because it causes a kind of sucking/draft effect through the barrel when the gun fires, so that gasses from the action doesnt get blown back into the bunker.
Tanker variant.
Less than 1000 were made, each one was handfitted.
Essentially works the same way as m321 port gun.
It gets attached into a ball joint porthole with a pin in armored vehicles.
And since its small it was supposed to work as the tankers weapon, being better than just a pistol.
There were a few suppressed ones that were specially built for very few individuals who needed them.
One of those being Lauri Törni, who fought for finland, germany and then for the US in vietnam.
Soviets made ppsh based on the suomi KP, in a more powerful caliber, but they had difficulty producing reliable drum magazines.
Rumor has it, a red traitor smuggled original plans of the magazine to soviet union, among with other shit.
EDIT:
The korsu version DOES have sights, theyre on the side.