Has anyone tried the Kai Seam Ripper?
Well, I asked that since I had ordered one and now it has arrived. I tried it on a casing for elastic that needed replacing. It works but you do have to be careful not to cut fabric. The elastic casing was wrinkled, of course, so probably more challenging than a flat seam. I pinned one end to my ironing board to create a "third hand" to be able to stretch the casing flat. Started an opening with a regular seam ripper large enough to insert the Kai. It was awkward at first, but with practice, it worked pretty well.
If you have long flat seams to open in a stable fabric placed on a flat surface, it would be faster than other methods. Not my first choice for thin fabrics or knits, for sure. It's basically a razor blade with a plastic frame around the blade to lift the fabric apart as you go.
I wouldn't bother to replace it if lost.