Before I retired as a federal agent, I used to train in Muay Thai and BJJ, mainly to stay in shape but also to learn how to strike with my knees and elbows (Muay Thai) and techniques if I suddenly found myself on my back (BJJ) with someone on top of me. I also earned a black belt in Combat Hapkido which is a version of Hapkido without any of the choreography and it focuses more on chokes, wrist locks and arm bars. I did Krav Maga for a while.
Like others said above, any martial art can be helpful from a conditioning standpoint but can also train bad habits for the real world. I have seen officers making an arrest who had training in BJJ be way too willing to go to the ground where now you have at least one weapon involved (the officer's pistol) in a grappling match, much less when there is more than one adversary.
I thought Krav Maga was pretty good for what it was created for. It was never created to be the ultimate fighting art, but rather to be a self-defense style that could be learned in a relative short amount of time by people of different ages and physical abilities. That is why it uses eye gouges, throat punches, groin shots, bending fingers, etc. A trained MMA fighter who is experienced in striking and ground grappling will have the upper hand on a person who has practiced Krav Maga for two months. But I think a person will learn more useful skills to survive a violent encounter in two months doing Krav Maga than any other martial art.
I had to go hands on with an adversary on a number of occasions during my career, including several times when a person pulled a knife and it happened so close that i didn't have time to use my pistol and used a Krav Maga knife defense technique. I also used a BJJ guillotine to choke out a drugged up steroid gym rat who outweighed me by about 50 pounds, was 8 inches taller, and 15 years younger, there was no way I would have been able to fight him stand up toe to toe. So different styles can give you tools to use, just beware of getting so conditioned to go to the ground, or not going for the eyes, throat, etc, since most sport fighting prohibits it.
