Just a few random thoughts to further muddy the waters...
1) Forget folders of any description for defensive use. Their deployment depends on fine motor control, which you almost certainly won't have in a life/death situation, and they are subject to failures of the lock and blade/handle joint under extreme use. Fixed blades are far easier to deploy, far stronger, and lack the vulnerabilities of folders. With a well thought out sheath and intelligent carry options, a fixed blade is concealable and yet readily deployable.
2) Do NOT take advice on legal matters (or really anything else of consequence) from gun store commandos. I have heard so much outrageous misinformation and outright falsehood from guys in gun stores that it's a mystery to me why anyone would trust their word. This especially pertains to legal matters. When your freedom and financial security depend on accurate information and informed analysis you'd be far better advised to consult a criminal defense attorney or a local prosecutor.
3) As has been previously alluded to, having multiple options is a good thing in a self-defense situation. There are times when you need to go straight to the nuclear option. There are also times (probably a lot more frequently) when having a range of choices along the force continuum is good. Not all encounters justify lethal force, and if lethal force is all you've got then you're at a distinct disadvantage.
4) If you carry a gun you really need to carry a BUG as well. Guns are mechanical devices that are subject to failure just like every other mechanical device, and Murphy dictates that they'll fail at the worst possible time. If you really do need to go nuclear on someone's butt you'd be far better off with a 642 in an ankle holster than a blade of some sort stashed somewhere.
5) No matter what you carry or how you carry it, REALISTIC TRAINING is absolutely necessary for successful self-defense. No one is born knowing how to defend against a violent attack. Simply possessing the tools to defend yourself doesn't make you any more capable of self-defense than watching kung fu movies does. Most martial arts are of limited value in life/death encounters, since they're more geared towards competition than actual combat. Realistic training necessarily involves LOTS of sparring involving different defensive scenarios. With any kind of training the thing you have to bear in mind is that the big difference between training and actual combat is that in actual combat the other guy really is trying to harm or kill you, and isn't going to pull his punches, allow you a mulligan, or hold back in any way. You also need to have a very good understanding of your jurisdiction's laws regarding the use of deadly force, and you should stay current with recent decisions regarding deadly force in your jurisdiction.
6) The defensive use of knives is a complicated business, and you shouldn't assume that you can just wave the blade around and prevail over a determined opponent. Don't let simply having a knife on you give you a false sense of security, and realize that the other guy might well have more training and experience than you do.
We now return you to your regularly scheduled programming. Carry on.