Thank you for this information
EDIT: Ok, I read that and I still don't know what does "mystery tradition/school" mean in this case (There is only stated that it is a Mystery School..). Generally "mystery tradition/school" means usually that sth is available only for those who are initiated into something (and OBOD course is available for everyone interested in it, and we are only asked to make self initiaton (which of course can be very meaningful, but it's not typical for "mystery traditions/schools" as far as I know)) or there are some mysteries involved - like Eleusian Mysteries and so on. For me personally mysteries (I mean these ritual experiences - it's difficult to distinguish these words, because as I see there is one word in English for these two things - mystery - sth hidden, and mystery like Eleusian Mysteries - in Polish we have to different words for this) are not only in great rituals but also in very simple things, each day. Seeing sunset can become great mystery, drinking water, and many others ordinary things or experiencing ourselves in many ways. Maybe it has to do sth with this?
This is really interesting for me, because term "Mystery School" is very "trendy" these days and I wonder if in this case it really means something or is just a nice expression.