The concept is good, but the design looks a bit flimsy - would those posts hold up?
If you gave the design a clear acrylic spine with holes drilled in for accommodating those posts, plus reinforced the structure with a strong adhesive, it would work better.
Suggestion: let's say you want to slip a deck in that's a bit too thin. If it was a metal clip, it's a simple matter to bend the sides inward a little to accommodate the skinny deck. If there was a way to adjust the walls of the clip to different distances apart AND provide adequate pressure, you'd really have something there. But you wouldn't want posts in all four corners - the evenly-applied pressure over the entire front and back of the tuck box would crush it unless the cards within were a tight fit to the box, which they rarely are.
Also, and I've suggested this before - acrylic is not very scratch-resistant. It practically attracts scratches, in fact. While few things on Earth are scratch-proof, you could try Corning's Gorilla Glass - almost all touchscreen smartphones use it, and probably some tablets as well. Alternately, you could make laminated covers in a pliable plastic material - the softer material would be more likely to "squish" under something causing enough pressure to scratch, and even if it does get mucked up, you can simply peel it off and apply a replacement, just like a smartphone's clear laminate covers.
EDIT: just had a good idea.
Make the acrylic spine I suggested, but put the posts a small distance in front of the spine rather than in it, and make the sides attach to the spine using a more flexible material. If you make the posts adjustable with something like a precision screwdriver, the clip would be adjustable to clamp down on a wide variety of deck widths. Making the sides meet the spine at 45-degree angles would probably make the ability to adjust easier to accomplish.