The clip went on my paterson 8x10 neg proofer after maybe 2 months of use (though the item was secondhand but "like new in box"). My 1920s splitback frames I use for alt processing haven't broken yet, but since I use them for alt process printing-out, they're more invaluable for the being able to see when the exposure is enough. I've not bought any of the new printing frames out there.
Also with the proofer I think that a full 8x10 would have a mark at the bottom left by the metal clip.