Yeah it's pretty clear they're not the best. Chain popped off about 6 times today. However that's almost certainly due to the hideous tension rather than the sprocket.
I guess I could set up an eBay alert thing for 6-bolt sprockets and get a better one, I had just assumed they were uncommon.
Fair enough: considering point c) ("horribly", rather than "slowly"), I concede*.
*I found the shape of Gusset teeth didn't mesh well with my chain and Gusset confirmed that certain combinations were troublesome.