I've never seen one that didn't have a strong magnet.
I have a hobby where I've probably opened a hundred of them that lived outside in the weather. I've never damaged a container opening one. They can be a little difficult to open, but if you use Helen's procedure it is fairly easy to open. Press your thumbs on the middle of the picture of the key and push the sliding lid away from you. Try to put your thumbs one in front of the other so you put the least pressure on the edges that slide. Don't try to use the ridged grip, that will press the lid against the body and make it harder to slide. Occasionally I run into one that's little stiff, so after I get a small opening I put something in the opening and twist it to open it more. After that it usually opens easily.
The feet do rust out doors and you have to replace them occasionally if your fastidious. I've never know one to stop holding, rusted or not.
It would be better if I could add a video but the picture I'm adding will have to do.