EdNJ said:
It's the serrations on the wrench flats,and it's not a gimmick. Matco sells something similar called Opti Torque or something.
It's common on the box-end of wrenches and on impact sockets. Snap on, Mac, Matco, Cornwell... they've all got it.
On the open end, Snap-On's Flank Drive Plus and Matco's Opti-Torque are the only ones, as far as I know. The Matco version only works in one direction, though. If you have to bring the wrench in there 'backwards' to break a frozen fastener with the open end, it's just an ordinary wrench.
That said, they very much do work. I ocassionally service things like jam nuts on tie-rod ends that you HAVE to use an open-end wrench on, and they're frozen. We have a cheap mix of everyone's Gearwrench, Husky/Kobalt, and Craftsman wrenches lying on the alignment rack. When I've got a stubborn tie-rod, the jaws on the craftsman will spread and round-over to the next side of the hex. The Gearwrenches and HD/Lowes stuff are a little bit better, but if it's stuck, I grab a Snap-On or Matco wrench of the appropriate size out of my box and break the exact same fastener free pretty most of the time.
I don't have any flank-drive plus snap-on stuff yet, but I'm eyeing some. The guy in the bay next to me has about $350K worth of Snappy, and I've used his notched-jaw wrenches out of curiosity. They do seem to work a hair better.
Mostly, you're paying for good steel. And yeah, a jewelry-like finish too. Most wrenches (craftsman, etc) are a cast material that, when broken, looks like pot metal - it's very pourous and a dull, matte gray material. If you've ever snapped a snappy wrench or ratchet, it looks like it was machined out of a piece of bar-stock or something. No porosity and much shinier inside.
Personally, I'd rank the ones I've used this way:
Snap-On
Matco
SK
Gearwrench/similar
Cornwell
Craftsman
Pittsburgh/Harbor Freight/Pot Metal
Before you ask, if the high-dollar Snappy wrenches can't get a stuck tie-rod free, I go grab a $20 Rigid pipe wrench, and bust it loose that way. Home Depot to the rescue...