These are basically a diy version of the jar openers I had as a kid, discs of rubbery textured material with various bank logos on them (my mom had a long career in banking at various small startup banks in the area). My experience with them is basically the same as yours, if you're having trouble opening the jar because your hands are adequately moisturized (hand lotion is great) this is a good suggestion. And slippery hands is probably why that jar is tricky unless you have hand mobility issues.