My DS is in CAP as a cadet. It is very much like Jr ROTC in many respects, but, as other posters have said, with a greater emphasis on emergency services/ search and rescue training. They also have a emphasis on aerospace education.
All that aside, I feel it is a better option than JrROTC because (at least in our area) JrROTC is a school activity run during the school day. It is a level 3 (not college prep) class. One who is intending to go to a competitive college or Academy really can't afford to use school hours on level 3 classes that are not mandated. One needs level 1 and 2 classes for college prep. CAP is run in the community (outside of the school day) and is an extracurricular. Hence, one can gain the JrROTC experience without watering down the High School transcript.