I have one of those Mr G. They’re brilliant.
If the lid edge is sloped I find a bit of pressure bites the teeth into the metal.
Yes, it will get into a lid that way, but a jar of Tesco Pasta sauce, (...er ... I know I make the stuff normally, but it had been around for so long I wanted to use it to get within two years past its use-by date...:0), had quite a strong lid, sloped as you describe, and because of its age - ahem - I had to resort to a cold chisel out in the shed!
It was just fine, and I froze the rest too!
