Id think it would be worth it even over 1 year for you depends how often you go to the range. When i broke it down i was going to save $50-75 per 1,000 rounds. Of course this is all if you even decided to get one :)
i think there called x-grip if i run into it again ill post it up here for ya. I think what it does is it makes a full size mag fit into a compact with extra length added to fill the grip.
edit google'd it and i was right x-grip is the name
http://x-grips.com/products/sw.html
well i ordered up the storm lake barrel conversion from STORM SW M&P COMP 40SW TO 9MM CONVERSION Storm Lake Barrels Barrel 9MM 3.58" Stainless Conversion Barrel Converts 40SW to 9MM S&W M&P Compact SW-MPC-9MMC-358-OP-00T
and mags from
https://www.44mag.com/product/692/smith_and_wesson
havent...