I took Krav Maga for about a year, while at the same time studying mixed martial arts (Brazilian Vale Tudo), with an emphasis on Brazilian Jiu Jitsu. Also have been studying Judo for about three years.
( I received brown belt in American Shotokan many years ago, but dropped it. Studied other Japanese karate since, but dropped them as well. Not enough tough, competetive sparring. Too many drills chopping air or working with compliant drill partner).
Krav Maga is basic punching and kicking, with use of elbows, knees, etc., with an approach of unloading everything as quickly as possible. Lots of focus on combinations. At the advanced level, they teach multipile attackers, gun and knife defense (but not much knife fighting), etc.
Biggest drawback of Krav Maga, from my experience, was lack of extensive training in take downs, grappling and ground submissions. Also, as in the karate I took, not much room, at least for beginners, in serious sparring.
In Vale Tudo (basically, mixed martial arts), we train without a gi, and go through a gamut of skills: boxing, kickboxing, grappling (Greco style), take downs, groundwork and submissions, with the emphasis on ground work.
I have done serious sparring (e.g., they don’t kick my head, I don’t break their arms) with advanced (black belt) Tae Kwon Do and mid-level Krav Maga fighters and other Asian systems (Shaolin karate, Aikido) , and I have always bested them, and not because I am such a great fighter. The main thing is that in most systems the fighters keep a space between them we call “the striking space”. In VT and BJJ, we learn, like Krav Maga, to close in quickly and eliminate that space.
The KM people are just not trained well, from what I can tell, in take downs and take down defense. One green belt I sparred with was stunned when I caught his leg on his initial strike. True, he punched me in the mouth during the take down, but within seconds he was on the ground choked out.
So, from lots of experience in many martial arts, if you want to learn how to fight, quickly,efficiently and well, study BJJ with a mixed martial arts emphasis. You HAVE to know how to take it to the ground and submit someone there.
The only down side is that VT and BJJ is tough – I have been injured several times, and usually come hope with bruises, lumps, scrapes, etc. I have also had to get in really good physical shape, including cardio, strength but especially being limber.