Someone correct me if I'm wrong because my Saiga didn't come with a BHO, but I believe it is just for holding the bolt open for convenience. I don't think it has anything to do with making it easier to change mags. I don't think it holds the bolt open after the last round is shot either. I THINK that you can get mags that can do that. There are quite a few threads about a LRBHO (last round bolt hold open) magazine. Long answer to a short question.
Yes, you can buy a pre-modified Tapco FCG from Dinzag.
"do the standard 30rd mags suck that bad that i should look at for sure doing