I used their Flight Engineer prep video prior to my written. I found it very useful, though John King's delivery is rather...odd... to me. Martha's segments are ok.
A better way to prepare for a written exam (if that is your intent) is to watch the video and then go over a Gleim or similar manual for a different set of explanations--ones that are a bit more substantial in most cases than the verbal pnemonic devices the King's use.
My 2 cents!
