No, the 50 is not RAZOR sharp,
Heh, heh. Good one. The 50 1.4 Canon I owned put every other lens I've ever shot with to shame. If I didn't need the $ to buy another lens, I never would have sold it as it was the gold standard for IQ of all the lenses I've ever tested.
First, Sigma is not an "off brand" which implies a cheap alternative equipment source for those buyers who are not serious or who can't afford the "real thing". It is a well respected 3rd party manufacturer and it's current offerings have been receiving literally rave reviews from well respected testing groups as well as consumers.
Touchy, touchy aren't we? Relax. We all know why folks buy Sigma and Tamron and Tokina lenses. Let's not kid ourselves here.
That being said, the sigma 30 has awesome iq for $300.00..
Where are you finding it for $300? I assume that's used? B&H lists them new for $500. To me, that's a pretty expensive normal perspective 1.4 lens.