I can't speak to any other brands, but Mr Gasket looks like the exact same steel gasket that Mopar Performance sells, but Mr Gasket puts a high temp coating on them (looks like aluminum paint). I have had both and had them side by side, right on top of one another. And you will always need to use a little extra pressure to slip it on the right side dowel pin for all of these gaskets.

Mancini is using the exact same picture on their site for the Mancini gaskets and the Mopar Performance, I'd be willing to be they are the same. The gaskets I have don't look like exactly like either though, they look exactly like the picture Mancini is using for the Superformance gasket with the larger rectangles for the cooling passages.