Changing mags on a Saiga is faster than stuffing a round into a tube
This may be the case, but it means you have to carry a lot of mags or spend time reloading them.
For example, in a duck blind, I can fire twice, and quickly stuff 2 shells in the tube, and I'm back to the three I started at, all with my firing hand still ready to go if another bird comes in.
To do the same with a Saiga, I'd have to have a stack of 2 round magazines set up, or I'd have to drop the mag, put a new one in, and probably use both hands to reload the mag I just took out. Plus I'd have to keep up with a magazine in a duck blind, which seems like it would quickly end up in the water or the mud. I've fumbled shells into the water and mud as well, but even at today's shell prices it's a cheaper loss than a Saiga mag.
OK, some good stuff. But why do people cling to their Tube Feeders if Saigas are so superior?
Hunting and clay games, or at least those are a couple reasons. Saigas have a lot going for them in the tactical world and in many gun games, but high capacity detachable magazines are far less important in hitting flying birds or clays than how the gun fits, swings, and balances, especially since laws and rules tend to limit the number of shells you can use.
Different tools for different jobs.