In my mind, the only real liability of the large is the potential for negative reaction from people who might see it as excessive, or as a weapon. Since that potential has proven itself to be low in my life, the Large's additional length of cutting edge outweighs it.
I can see where the Small would be more practical for someone who had small hands or small pockets. I'm medium in both respects, and the Large doesn't present a problem.
The mythological Medium Sebenza would probably be ideal for me as an EDC. I think people have correctly observed that Chris kind of hit above and below the sweet spot with his two sizes, but given that the idea was to have two sizes, they seem very well calculated. If there were only going to be one size, it would want to be between the two. If there were going to be three sizes, my guess is that the middle one would be the most popular.
Three sizes are much more interesting than two from the collecting standpoint, but I tend to look at the Umfaan as part of a trilogy in this pattern.