I have one. Pics are around the site if you do a search.
It can be practical, but mag changes aren't quite as fast as you'd think- with no last round bolt hold open and it being a shade cumbersome to swap in a fresh one with the bolt closed (still faster than reloading a full 6-8 shot tube mag, but not quite AR-15 fast), you'll have to practice with it.
Accuracy isn't bad- no worse than any other shotgun. The hard part is that the "sights" on the thing have a ridiculously short radius (maybe a foot), so it takes some getting used to. If you do a pistol grip conversion to make it more like an AK, cheek weld can become an issue, but it isn't the end of the world. I've used mine at the skeet range- works ok, not great, but ok, and the looks you get make it all worthwhile.
Reliability isn't bad- much depends on how well yours is made. There are "vodka specials" where too many of the gas ports aren't open to the gas tube, but mine is fine (there's 4 total ports, mine has 3 open, and that is enough- if yours doesn't work, there is a US company doing warranty work). Mine (I only use the stock 5 round mags, and you do have to fit them to the gun) can tend to run a shell into the top of the chamber instead of putting it into the chamber.
The stock mags are 5 rounds, but there are 8 and 10 round regular magazines made as well as a 20 round drum.
For home defense work, I'd probably reach for my 870 Tactical first, mainly because it doesn't malf- ever. The S12 can.
If you want more S12 info than you ever wanted, check out the Saiga 12 forum.
