I am decided not to spend those thousands for the prep course. Language is one thing you can work on by watching english videos, reading books etc.. I think those course are suitable if you don't have lack of couple thousands USD and you have problems in setting reading schedule and keep that schedule.
On the other hand it seems to me that you can handle the information in the books and can see by yourself which of the info is needed and which aren't so I wouldn't spend those money.
So I have decided to stand alone and spend the money for something else