Krav magra is a really interesting modern martial art. For my taste I prefer martial arts that can be practiced for a lifetime without scarring bones joints tendons. yes it's effective however other than the fight dirty mentality it's not proven itself to be any more lethal hand to hand combat than any form of martial art. It has a different mentality and that's the limit of the advantage imho.
compare that the the fighting styles of Korea, Japan, Brazil, China and you'll see fighting systems that were designed to fight wars hand to hand. (Shaolin monks fought off multiple attackers with knives swords and spears.. Yes their dedication was second to none not to simplify the Monks ability.)
21 foot rule is something I was taught in the military and after the military in personal security. If the gun is already drawn and aimed..no your not going to beat his finger. The trial or test is can you draw and fire a shot before I can get to you with a knife or punch. The answer is no! Look it up and you'll find information.I know most people believe that a gun wins all but surprisingly it's relatively slow to draw and aim.
First look up how many shots are typically fired in a fire fight and how many typically hit any targets.(I don't include targts shooting at cars with 100 rounds they might as well just throw a grenade inside but hey..
Then look up how many police officers have been shot with their own gun from an unarmed assailant.
Mui Thai is extremely effective 1v1 but you don't see it in mma for a reason. Tae Kwon Do and Mui Thai and boxing among several other sports are very limited in their attack methodology.
UFC and MMA fighters are good tough guys with solid conditioning and a well trained punch. Good wrestling basics,2 kicks to their repetoire and a desire to be famous.
The most lethal fighters in the world aren't allowed to use their normal attacks in UFC and MMA type fights. WHy? because most of those attacks were originally designed to be maim and destroy, which is why you don't see their styles/tactics or disciplines represented in MMA and main stream media.
P.S. the reason I don't watch the MMA stuff and UFC stuff anymore is...well..watching 2 guys spend 5 minutes rolling around on the floor wrapped up in each others legs to try and get the other one to tap out? Now female greased pig wrestling!! that's a sport