Concept of a balisong is pretty good, but in my experience most of the ones I've come across are made for tourist crap. Action isn't any good, metal rusts like mad, either too stiff or a little flimsy.
I did pick up a pretty good Chinese made one (Rostfrei on the blade) when I was in the Philippines a few years ago. It's all metal, doesn't rust and has great action. It's the exact same one that was being sold as a trainer by Jeff Imada (except the trainer was ground dull - I also have that).
Balisong are illegal to carry where I live in California - as they're considered concealed weapons under California Penal Code 653(k), I believe*. They're clasified as a switchblade or gravity knife - though you actually use inertia to open them - but lawyers don't know physics.
As a general tool, I'd find them impractical, as they tend to be pretty long, don't fit in the pocket well, and have no clip. For self defense, they're flashy, but take too long to deploy (and I'm pretty quick with it) - and are illegal to carry. Want to explain to a cop you were defending yourself with an illegal knife?
Personally, I usually carry a small locking folder - 2 3/4 inch SpyderCo Delica. I have a half serated and full serated blade. I like the serated blades as you don't need to really sharpen them often (or ever it seems) for them to keep cutting.
I'm usually opening a lot of boxes and packages at lab (sterile equipment requires a lot of disposable stuff - so lots of boxes). Also great as a camping knife - cuts rope well, thin branches (serated is no good for wittling, though). It's a great tool.
You could use it in a pinch for self defense, but running or giving a wallet is probably the safer idea. Nice thing about a short blade is, they're practically impossible to disarm. But you also have less reach.
It opens really quickly with a flick of the thumb, has a built in clip (new ones you can switch the clip to right or left carry). It folds down to 3" for a comfortable in pocket carry.
I've heard there are two kinds of people - those who carry knives and those who borrow them.
*California's "Dirk and Dagger" law (code 12020 (24) I think), defines any instrument that can be used for stabbing and causing great bodily injury a dirk or dagger. That was changed to allow LEO (law enforcement officers) to arrest gangbangers for carrying ice-picks and screw drivers. Unfortunately, the wording of the law could also apply to a sturdy pen - but I've never heard of anyone being arrested for carrying a pen.