Well, I don't want to be involved in an argumental cat fight, but;
Crucible Steel is just one manufacturer of SS barrel steel, and the steel they are offering is just another marketed name for one grade of steel. There are others, like OutoKumpo which is one large worldwide supplier of SS barrel blanks, and they also have their own "special stainless steel" names such as 416RQ, 416FQ and 17-4.
Sulphur in SS does not help against rust but a lower level helps getting rid of "red-short" which usually makes the steel brittle when worked at red-hot temperature. The smelters usuually compensate the sulphur content by adding manganese but that's another story.
The rust occurs because the coating is somewhat porous, but it does not mean the steel isn't good. As for machining, the 400 series is not so easy to machine, and no manufacturer of SS rifles is exempted from machining flaws (see the Winchester ones...) .
AFAIK no one ever said that the Zastava SS rifles (and even any other of their products) are the best and well produced, but for the price, they are hard to beat. And it' easy to compare two similar products one being over twice the price of the other, but to me it's somewhat pointless as there are obvious (anyways, it should) reasons why one is priced how it is...
And honestly, myself, I bought a Zastava SS to be a beater rifle, and I still have to hear about one failed SS barrel - maybe there are somewhere, but I never heard of them.