I live in OK and I don't see them worry much about knives unless they are automatics. If you are caught with an auto you go to jail from what I've been told here where I am. I've read the law but bowie knives, metal knuckles, sword canes, and other such things can get you nailed here also. The problem with some of the descriptive terms in the write up is typical because dirk knife is one of those hard to pin down terms usually. Ask five LEO or the Sherrif and a couple deputies separately what a dirk knife is and you will get different definitions from each one. Same with autos. Some consider the Kershaw assisted openers to be autos and others don't. Which is primarily why I don't carry one a lot. Get the wrong cop and off to jail you go to plead your case to a judge.
I don't see a legal limit listed for blade length here in Oklahoma and personally know many guys carrying folders with 5 and 6" blades but that doesn't mean you can be reckless about it. I think common sense is your best bet to safely carrying the folder you choose. It seems to me there is some benefit to statements in the law like, "except this section shall not prohibit: 1. The proper use of guns and knives for hunting, fishing, educational or recreational purposes. The key words here are proper use. Whipping out your six inch blade at the mall is by most definitions not the proper use of your folder. Nor would it be the proper use of your folder to have one that big on you on the way home from the local pub after six or seven beers. So long as you are not stupid about it you should be safe.