I call it the Magic Device! If it's not branded it's possible you might have a copy, and not sure they're as good. The Leifheit one surprises me, because I would have thought it'd need a lot of grip from the user to work effectively, which might be counter productive. Never got into silicone mats, but discovered anti-slip matting for drawers etc rather effective for fountain pen disassembly* so tend to have a square of that handy for Sieger-less situations. Of course, if worst came to worse, it'd be down to the workshop and into the vice jaws. That really works.
*Now that has produced situations on a par with WG's pickle tackling. Once spent a whole afternoon, and lots and lots of swear words, trying to get the hood off a Parker 51. Ended up with actual blisters on my fingers as a result, but we got there in the end. That was an "Isn't Life Great" moment, because then I could repair it, get it on its way and never see the ruddy thing again!
To be honest, it looks identical, and there's not much to go wrong with a big rubber band really
Mine came from Boots about twenty years ago.
The Liefheit one works easily if you make sure that the lid you're trying to open is properly fitted into the ring part, and then it's simplicity itself. It's still best used with a silicon mat, or a bit of the drawer liner foam cubey stuff, to grab the jar itself though.
I have small hands and even I manage that one, and I can't work most pruners for long because they're too wide.
Do the vice jaws not leave such a mess though ? stuff leaks when it's on it's side to open.
The drawer liner stuff (or rug gripper stuff) is very good a couple of handspan sixed offcuts and it helps shift almost any lid
I have one gadget that's been so brilliantly useful that I bought half a dozen of them and gave them to friends.
From opening ring pull tins to bottles, even sauce bottles, it's excellent
My friend broke her elbow, on her dominant hand, and I gave her one of them, and she said it was such a kindness because she could manage without pestering anyone to come in and help with little things.