I frequently train this aspect of knifework. One of the most important and yet overlooked aspect of using a folding knife in combat is deployment. I don't care what you've got, be it in your trunk, safe, pocket, holster, etc if you can't get the damn thing out and into your hand in a usable grip, you're just playing with yourself.
Drawing a closed folder and then striking with it is a great way to either off balance your opponent and/or get the position, distance, and time to open the blade if necessary. I've found that with many folders, after striking with them pocketstick style the best way (best=read "economical, speedy and secure") is to use the thumb opening and go into a forward grip edge up. Utilizing this grip has a shorter count of movements in that you don't need to re-orient the edge, which leaves you with a rather tenuous grip on the knife. FGEU has other interesting capabilities while fighting, but the best aspect is speed and security of blade deployment.
One knife I have that works excellent as a pocketstick is the Emerson CQC7. Feels good in the hand, has a somewhat symmetrical design that allows a secure grip, and it opens quickly and securely. Hammerfists, edge of hand blows, reverse hammerfists all work great with the knife closed in the fist. Adding a lanyard adds another layer of security that you should experiment with as well.