Did you know that your STEN is Ex Finnish? And did you know that this is one of the Mk2s that should have been recalled for destruction towards the end of WW2? It uses a wrap around body, i.e. the body is formed by forming sheet steel around a mandrel, hence why the sides of the trigger housing are all one item with the body. Because the sheet steel is thinner than the trigger housing of the weldded tube Mk2s, they had to place a spacer and repositioner on the trigger housing. This makes it a unique feature and although not really rare, they are quite a scarce varient to find so well done.
Your other STEN Mk2 is also very nice, it looks like a Enfield Made gun and also the No.2 stock is quite scarce with the reinforcing bar.
Not really a lesser quality item, it was an atempt to make production simpler but the idea failed because of the way they were made (the bodies opened up). Lines Brothers shared the same idea but got it right with the mk3 by having the join at the top and running the length of the body, preventing the spread.
The reason behind the butts is again simplification. The T butt required 5 parts, the stud, the abutment plate, the tube, the pistol grip bit and the butt plate, these also had to welded together. The wire stock requied 2 parts, the abutment plate and the U section shaped to make the butt shape and this only required welding at one point.
Very interesting,you mentioned my skeleton stock was unusual with brace,was there a time line for all these different stocks and did the wrap around body type have a specific name [other than mk2] that can identify it for the future,thanks for your expert knowledge.
The brace appears to have been only fitted to the early skeleton stocks and then discontinued, perhaps as it wasn't required due to the strength of the stock without it. The wrap around body is well known by that name, the easy way to identify it from a distance is the repositioning plates welded on around the selector button. If you want a good read, keep an eye open for the 'STEN Machine Carbine' by my good friend Peter Laidler, its not cheap but it is the STEN bible.