Rayhzel, the main differences between the two books are that the original KBM has one program in it that lasts 12 weeks while MKBM has I believe 20 programs in it. Some last six weeks, some nine, etc. There is also variety of programming types in MKBM, such as Olympic style complexes, ballistic style, some focusing on grinds, etc.
I really like MKBM and have done two of its programs but my preference is the original, as I like the structure of it and the fact there is no thinking about exercises, exercise selections and rest periods.