Anyone have any experience with VARYCON VC filters? Comments? Problems? Results?

These are/were made in Croatia by FotoKemika. I've got a new, gelatin set marked 0-1-2-3-4-5 in 12" square. The colors look like my Ilford VC filters. I assume they come/came in other sizes. I have no idea what equipment would use 12" VC filters, but I assume they will work fine for me.