I've bought a few times with the seller and once you understand how they list items they aren't too bad to deal with. Most of the sanitary stuff they have is listed by the od of the flange, which really isn't standard practice. A 2"(50.5mm) sanitary fitting has a 64mm flange and a 1.5" (38mm)fitting has a 50.5mm flange so you really have to pay attention to how they list things. The fittings they have aren't that different than you will get from Stout, Glacier, Bobby or many of the other vendors sourcing their stock from China, but the US vendors will have things spelled out much better.
OP, What you linked is not the fitting you want for a direct connection to a keg unless you are having a 1.5" sanitary fitting welded into the bottom of the keg.
If you're looking for a one stop shop to get only a bottom drain setup, Bobby is probably your man, but if you're buying a ton of fittings then it might be worth looking around at the different sources.