These would be the same dimensions (besides thickness) of 3 base cards...plus additional space due to the tabs that connect the three cards together. The Ultra-Pro double landscape booklet would not work because it wouldn't be "tall" enough and the other Ultra-Pro wouldn't work because it wouldn't be "long" enough.Can you post dimensions? If I am not mistaken, they are the same as the bi-fold horizontal booklets. If that is the case, the Ultra-Pro double booklet one touch would work beautifully and are not crazy expensive.
It also depends on how we as collectors keep our cards. For me, mine aren't ever on display...just protected and put into a box to rummage through once in a blue moon. These unique size cards fit closed up with cases already available IE: 25 count holders such as this: https://www.ultrapro.com/product_info.php?products_id=651&osCsid=661jlmnhne6u6kvnid69i99i71 and by adding a piece of foam or something to ensure it is not moving around inside. Those that want to display the card out in the open, I think it is worthy spending the price on a custom holder if that is the intent, similar to having a budget for framing.These holders are expensive but I guess the cost of designing and mass-producing things like this is greater than I would suppose. I remember PSA for years dragged their feet to create holders to accomodate all the new cards of varying thickness. They said it was just too expensive for the number of submissions they got that would require them, but that seemed like a chicken/egg problem. I mean, you have the top/front half that can remain the same, then varying depths on the bottom/back half of the slab. Shouldn't be too hard, I would say confidently as someone whose never fabricated anything or run a business like that. But all these fancy folding cards, the Triple Threads tri-fold cards especially, by design, is not a large popuplation relative to normal 2.5x3.5 cardboard. You've got a couple manufacturers putting these things out, so it's kind of a small, captive market, and they can charge what they need plus what they want on them.