It seems that the biggest difference is not the agency, it`s the instructor. Unfortunately a lot of us don`t want to go to all the trouble (and it`s a lot!) it takes to thoroughly check out an instructor. If you don`t have a lot of time, nor a lot of experienced people you trust, this can be a pretty hard problem. Another thing to consider is the course. I understand there are some new courses and levels of certification that don`t really give you what you need to be safe. Everything I`ve learned about this subject indicates that the agency is almost insignificant; the instructor, though is crucial.