A couple points.
There is no 30 round drum for a Saiga 12. There are two 20 rounders available. You would not want a 30 round drum because it would be very big, and very heavy, and would put much more weight on the mag catch than it is probably designed for.
The Saiga is not the best shotgun of any category except the one in which it resides, which is affordable, box mag fed, semi auto that can handle most shot loads. It needs a large amount of custom work to reverse the neutering it received to get into the country, plus other treatments. The design is good, the materials are good, the quality control is variable.
I own some shotguns. I own a Saiga 12, a Benelli M4, a Remington 870, and some Mossbergs, along with Winchesters, Stevens, JP Sauer's, and others. I shoot clays with the 870, although the Saiga can hit them. I hunt turkeys with the Mossbergs. I use the Benelli for home defense and range fun. I shoot the Saiga at the range, as I have yet to covert it, nor run it enough to be considered reliable.
Is it a good gun? Yeah, it is, I like it, and it's worth the money I paid. I will enjoy converting it and customizing it. But, it will not be my only shotgun, nor my favorite.