I quickly skimmed thru this thread... so if this has already been mentioned, I apologize.
First, there isn't a problem with purchasing discounted gear from GearFest.
I went last year... and got a fantastic deal on a PRS guitar. It's flawless.
GearFest has turned into a HUGE event.
"Disneyland for musicians"

Millions of dollars in gear is sold that weekend.
Manufacturers give Sweetwater great pricing... knowing they're going to make significant sales.
Regarding both the SM57 and SM58:
An SM57 has no built-in protection against "plosives".
Any SM57 will "pop" if you sing directly into it.
An SM58 has a small bit of foam inside the grill.
That helps, but it likely won't be enough for strong "P", "B", or "T" plosives... where a lot of air is sent directly toward the capsule.