Not sure about the Rocklers, but the Jevons are square to within .002" over 6", which is why they can be used to square fences. I assume the ones sold by Woodpeckers are just as square.

The Woodpeckers are anodized, so they won't mark the wood. Obviously, the Rocklers won't leave any marks or scratches. I don't think the Jevons models are anodized, but so far they haven't left any marks on the wood, even a light-colored wood like maple. Maybe I've just been lucky.

The Jevons models have holes in them, so they can be screwed or bolted onto jigs.