Bram is right on. His Escalator is the modern replacement for, indeed the evolution of, the Bali-Song.
The key point to understand about a butterfly knife as a fighting weapon is that it's as useful closed as it is open. This is where a lot of modern folders fail. To use them as a weapon, you must open them, which takes time and requires at least some manipulation under extreme pressure, but it also requires you to jump immediately to an edged weapon. If an attacker throws a punch at you and you respond with an edged weapon, you have legally escalated the situation to deadly force. Your opponent may now, legally, draw his gun and shot you and he will be innocent by reason of self defense even though HE threw the first punch. On the other hand, there's a world of great responses with a closed Bali-Song that don't escalate to deadly force. Then, if the situation requires it, you can open the knife quickly.
A few modern folders have some if this. You can translate many closed Bali-Song techniques to Benchmade's AFCK with excellent results.
Rekat's Escalator (it's the perfect name for such an excellent knife), though, was designed with all of that and more in mind. My hat is off to Bram for this great design.
The big problem with a Bali-Song as a combat weapon is the complexity of opening it. Even simple techniques can be botched especially if you're nervious or have wet hands or are wearing gloves or maybe have had your hands slightly injured (scrapped up punching, for example). When you botch a butterfly opening, you often drop your weapon.
If I was to say one thing about the Escalator that is at all critical it would be that that I'd prefer it to have a thumb stud or Spyderco hole to more positivly open it. And yes, Bram, you have personally demonstrated to me several techniques for opening it, but I still don't always get it reliably.
As for butterfly knives today, I don't often carry one and then it's not really my weapon. You'll see my AFCK or my Escalator peaking up over my pocket. I just find butterfly knives very fun. I'm a habitual fidgetter and they're a great toy to fidget with.
As for the suggestions to tape or dull the blade, that's good for starting, but try to get over it as soon as you can because you will learn bad habits if you come to rely on it. Yes, if you start playing with butterflies, you are going to get cut. All I can tell you is: cuts do heal faster with Neosporin.