There's really nothing too 'compact' regarding shotguns. A SB shotgun ('legal') would be either in 18.5-20'' barrel length. You can legally posses a 14'' barrel SG if obtained via the proper laborious permit process. I have a Saiga-12 and it's rock solid. The only other option I know of would be the AR-15 like shotgun (outside of youtube, I have seen no reviews):
http://www.atlanticfirearms.com/storeproduct1000.aspx
-Cheers