Energy Gates is an essential foundation of Bruce’s system. It’s extremely powerful and I noticed an immediate improvement in my health and vitality when I started practicing it. I followed the sequence and time table Bruce outlines in the book and took several months to do through it as well as taking a couple years of classes in Boston in it.
Dragon and Tiger is a powerful chi gung system, but as I understand it (and please understand that I’m not a teacher or disciple of Bruce’s so take everything I write with a grain of salt) it’s good for general health, but comes from a different tradition than the other chi gung sets Bruce teaches. It’s definitely worth doing, but it doesn’t seem to me to be part of the core 16 nei gung that Bruce stresses in all his books and teaching.
I hope others will chime in here.