Neither really "squeeze" your deck at all. They are in the shape they are in - they aren't actively trying to compress your deck. If you get any pressure, that pressure comes from your deck being thicker than the space between the metal sides. You can adjust this by adding or removing extra cards in your deck. I carry most of my theory11 decks in a flat-spine Porper clip, and they are really tight if I leave all the cards inside. I remove (and frequently give away) the ad cards from my deck, and then the deck inside fits snugly without falling out, but is still easy to remove.
If you expect a Porper clip to flatten your deck, you are looking for the wrong sort of tool. More than anything these will just hold your deck flat preventing it from getting bent out of shape in the first place. It won't fix a warped deck. I carry my decks in a front pocket of my trousers, and the Porper clip helps extend the life of the deck.
// L