As an LEO I've never seen anyone charged for a "concealed knife". I'll admit it occasionally makes us nervous depending on the individual, but so would a screwdriver or anything else that could be used for a weapon in similar circumstances. There's no criminal charge for carrying a concealed knife of any size. It's simply not in the crimes code. The best someone could try and do is articulate it under the POW statute somehow and the case law isn't on their side in that. Case law hasn't upheld knife convictions generally.
A lot likely depends on what you're carrying and where you're at too I'd guess. A fixed blade double edge or combat type knife would likely draw more attention than a folder or a smaller fixed blade utility pattern. I still think you'd be hard pressed to charge someone for it unless they were doing something else wrong though.
No button, or spring loaded mechanism so the one hand opening aspect is moot. Nothing prohibits them in the least. Take a look at that 1979 case law you posted earlier again. It's been ruled on that a balisong is not covered by the POW statute according to that.
I've found knives on guys I've arrested any number of times, as have guys at work. I've never once seen anyone charged for them and they're given back to them when they're released.
The only caveat would be (and I know this sucks) if you get a cop who's overzealous about the issue or is reading more into the law than is there then you *might* run into problems. They'd likely get straightened out in the end but that doesn't make up for the aggravation to you. Fortunately those incidents don't seem to pop up too often, at least not around here.
I have an auto I use at work sometimes. Even with a badge I won't carry it outside of work. Not worth the aggravation. I carry an AO or OH opener or a SAK usually. Very occasionally a fized blade (unless I'm hiking or camping them I always have a fixed blade).