Yes..the 870 is a great choice, I have two of them, one is my main hunting shotgun with beautiful walnut stocks, so I wont be cutting that one down. My second is an 18 inch 870 HD model. Box stock with nothing on it but a butt cuff with 4 rounds of Hornady TAP buckshot.
I also have a yard sale Savage pump gun that had the bbl cut down to 18 inches before I got it. I put a slip on recoil pad on it, and I keep it stashed on the first floor with buckshot therein.
As for a SAIGA 12, I think a lot of it, but I dont have the cash lying around to buy one because I need to spend my gun money on 45 auto ammo, 9mm and a lightweight 38 J frame model 642.
The saiga is well thought of on www.warriortalk.com by the folks who are trained by Gabe Suarez. I also saw a former member of the Spetznaz named Sonny Puzikas who really worked over a combat course with a saiga with a 10 round mag in it.
I may get the saiga this fall if I can get my other wants taken care of.