I am putting in a new circuit in my workshop (bought a 12a shopvac and it
makes the lights flicker) so I need to replace a full size 20a breaker in my
Sylvania box with two half size breakers.

I went to HD and they had two of them, a non-current limiting breaker for
$15 and another one for $10. I asked the clerk what the difference was; he
said there wasn't any difference and told me to buy the cheaper one.
That didn't make any sense so I asked a guy in the aisle if he knew. He
didn't but after looking at them pointed out that cheap one has a little
contact and the expensive one had a big contact. He said the expensive one
can be used in all boxes, but the cheap one can be used in all boxes. That
makes a lot more sense, but still doesn't explain what non-current limiting
means.

So, does anyone know what the difference is, and which I should use.
Funny think is I have put in two others without encountering this issue
before. I wonder if I used the right ones??!