I had the same problem and tried the disk shaped cheap one, it would flow no fuel even under the lowest setting, this was with the facet type aftermarket pump.
So I agree the cheap ones aren't worth it.
I decided to rebuild my SU with some cyberhelp from Dave Dubois, who hangs out here on the BCF and has written some articles on the subject. I am pleased with results and the rebuilt pump has been ticking away merrily for a couple of months now.
I decided to put the old pump back in after a) experienching pressure issues despite the aftermarket pump being low pressure, and also reading several online comments from people that had experienced failures with their aftermarket pumps after 1-2 years or less. Since my SU had lasted 8 years before quitting (and who knows how long before that) and it presented no carb pressure issues, and if it failed there was a very good chance that I could fix it with roadside repairs I decided the cheaper aftermarket pump was really a false economy.