Phil:
For over a decade I carried a Gerber, light weight, lockback, with a 2 1/2" blade and a finger notch for a solid thrusting grip. I have small hands and the fit was perfect. The knife was light enough and flat enough that it would fit in my wallet, ergo, I got into every courthouse and airplane by putting my wallet in the tray and handing it to the security guard. It was easily snapped open with a wrist flick. The blade didn't hold a good edge, was a bit flimsy, but it was intended by me to be a last chance, close quaters surprise for a miscreant who would be dumb enough to think than old guy was no threat.
My Wife decided her husband should have a "special knife". She knows I am very security minded and wasn't carrying it to clean my nails. Nevertheless, for a birthday, she bought me a bone handled lockback folder from Col. Littleton. It has the same length blade, looks great (engraved with my initials, of course), excellent steel, holds a nice edge, and fits the curve of my hand (no finger notch). I guess, since it sits in my pocket, concealability is not really an issue. I will admit (when in NYC on empty streets) to carrying the blade open, hilt palmed with the blade up my wrist.
So, for the sake of my Wife's feelings I gave up my old friend, and I now carry a knife that weighs twice as much, won't open as easily, but, in a pinch would serve the intended purpose.