Hmm...I'm surprised at how many posts there are on this thread comparing HKD to MMA or "knocking" it's techniques by trying to validate it through an MMA format.
I've trained in HKD for 10 years, and one of my best teachers was also a very successful MMA style fighter. He fought in the Kyuk-Too-Gi (Korea's version of MMA) and won convincingly. I've also been training in BJJ and in Muay Thai, so I've seen the MMA "side of the coin" as well.
What I don't get about most of the people posting is that they're totally ignoring that HKD is built specifically to DEFEND yourself. Not GNP someone or KO them with 5 knees to the head. Self-defense can be as simple as breakfalling to protect yourself from taking a hard fall or using a joint-lock to subdue an attacker long enough for you to get away or to keep him from attacking you further. Anyone who's actually fought on both the street and in competition knows there's a strict difference between self-defense and fighting competitively. Just look up Alex Gong or Lee Murray and you'll find out why.
For the technique "pricks" who think that a martial art simply isn't good because one technique doesn't work for them, open your eyes because all martial arts have techniques that don't work for some people, but work for others. There are numerous BJJ techniques that my instructor has shown that the class definitely didn't like, but worked great for his game. That's WHY you learn more than one technique, so you can find out what suits you. If one technique worked all the time, I wouldn't be wasting time posting on this forum. I'd be making millions of dollars teaching my "ultimate technique" that works on everyone.
About a year ago, my BJJ teacher had invited Mestre Alvaro Barreto to do a seminar for us. Mestre Barreto had stated at the end of the seminar that he would love to do a more "self-defense" oriented seminar the next time we brought him back. Ironically, I asked my BJJ teacher about this and he said "Don't worry, it's pretty much like HKD...Anyway, I'd rather have him work sport BJJ instead..."