The answer to your questions largely depends on what context you are defining where Krav Maga 'works' - street, ring, ?
I trained in Krav Maga in the 90's before getting into MMA. And there was certainly limited sparring contrary to what some people are posting, including some limited multiple attackers scenarios.
Secondly, Krav Maga's general mindset is to simply do enough damage/distraction to ensure you can get away safely and then run like mad. It is for street safety/survival, not for winning in sport. (The battlefield variation is likely a bit different in that regards, but this was civilian instruction). Nut shots, eye pokes, nostrils as a handle, etc. are all taught. Its strikes are a very basic subset of boxing and MT (elbows and knees), and they brought in basic BJJ for the ground.
I would say it was the most 'realistic' of any martial art I have taken (i.e. compared to TKD, Tang Soo Do, Karate, etc), so if that is your question regarding 'does it work', then yes.
Its very much designed to take advantage of natural instincts, minimal training and ensure you can at least get away from a dangerous encounter forced upon you. Example - they found that by researching police reports that most rapists get the mount position and then choke the victim to force submission...hence, they spent a lot of time drilling basic mount escapes esp. with male trainees on the women to make it more realistic (i.e size and weight disparity).
And with regards to the whole 'rehearsed' aspect - after we learned a choke defense, we had a water break. While I was waiting in line for the water fountain and talking to someone, the instructor jumped me from behind with the choke we had been working on breaking out of, and applied it hard and full force until I got out using the defense we just learned. My throat was bruised for about two days, but the point of my mentioning this is to show they take it pretty seriously and will force completely unrehearsed suprises on you as part of your training.
That said, if you get into a hardcore MMA gym, the focus and intensity is going to be a whole different level, in exchange for a lot more training commitment. There were a lot of housewives and relatively out of shape people in my Krav Maga classes and thats more their target audience - normal people, not athletes and street survival, not taking someone out within the context of sport specific rules.
Anyway, that all said, you really should go watch or try out a class instead of making decisions based on postings here.