I have a switch-blade that is illegal. The blade is release by pushing back on the top part of the handle. I think that 90%+ of LEO will not recognize it as a switchblade. The blade can be opened manually, just like any other knife.
I have a Kershaw that is spring assisted opening, however, you have to push on the blade to open it. I think it is legal but I recognize that a LEO could disagree.
I dropped it once, going through a metal detector and it 'sprung open'. The LEO monitoring it, wanted to look at it because it opened so fast. I was able to switch knives and gave him the one that is NOT spring assisted.
No sense asking for trouble.