I own the Saiga 12 w/ fixed cylinder bore 19" barrel. I couldn't ask for more out of a semi-automatic shotgun. I purchased it back when EAA was still importing and sat on it until the sunset in which I immediately added goodies (folding stock and cut tang, pistol grip conversion, new fire control group, etc) AND made sure it was 922r compliant in the process. Iron sights were kinda junky and the sight radius poor so I opted for a Kobra and a raised cheekpad. Loading magazines isn't an issue at all open-bolt; it's just rock-and-lock. Closed bolt might be an issue and require some wiggling or aforementioned stimpcatch widget with an optional light shaving of the bolt (which I did both and works marvelously). Newer Saiga's come with a manual bolt-hold open.
8 round magazines can be found, but they're at, or very darn well near the $100 mark each STILL; there are rumors of soon-to-be stateside manufacturing of these but I wouldn't hold my breath. The stock 5-round magazine that came with my Saiga fires 3" magnums or 2-3/4" shells just as well without jamming or causing issues. You could even mix aforementioned shotshell sizes if you desired to and proceed to empty the magazine but there is a specific gas setting adjustment on the firearm that is to be used for 3" magnum loads (can be set with a coin and depressing a spring-loaded pin)
I've eaten boxes of Walmart 100-round value bricks in Federal 7-1/2 shot to Remington 000 buckshot, and upwards to Federal 3" magnum rifled slugs. The only problem I've ever encountered was two light primer strikes on PMC 00 buckshot I got at the range (can't recall if it was light or full load--cases were milky white/clear) encountered over two 5-round boxes before I gave up on them altogether. No hiccups on any mix of Federal, Remington, or ("evil") Wolf buckshot/rifled slug loads I've tried yet and I'm going to surpass the 1000 round mark soon. Besides, it's good sense that one test and use ammo that their particular firearm won't hiccup on (especially critical for a home defense setup).
The internals are what you 'd expect in an AK-variant--simple; I did all the work myself with nothing more complex in my tool collection than a cheap drill press with end mills and a vice. The only negative thing I can think of (since that is the thread starter's question) is that EAA no longer imports them and prices are starting to rise. That, and the aforementioned short sight radius on the stock open sights.
It's not uncommon to see Saiga12c/k's going for $1000 and conversions going for a few hundred less. I've seen plain unmodified Saiga12's running $400+. Compare this to the going rate of $199 apiece at CDNN back in September '04. Firefly Arms used to do a conversion for dirtcheap (IIRC a few hundred dollars including lots of conversion parts sans a few customer-supplied parts) but they've stopped gunsmithing completely.
All in all the thing is built like a tank and handles remarkably well. It might look ugly (if AKs are considered ugly) but tanks are built around function, not form.
Included is an image of my Saiga 12 cuddling with my "Molon Labe" Khukuri!