That is really like asking how playing baseball is different from snow boarding. They are both physical activities but that is the end of any similarities.
My experience with the SBG is certainly much deeper but I did teach a work shop at a Krav Maga school once. Perhaps if you told me your goals in training I might be able to help.
I did go to look at a krav maga class. I did not like the idea of signing a contract. I just did not know if it was all marketing. It was a beginners class that they were hitting the heavy bag. I also went to another place in my area that taught western boxing. I was very impressed. I have one more place to visit and that is a straight blast gym. My goal to find a place that I like.