The course creators cite some research but I haven’t read the original articles.
There are some very simple demonstrations on why the usual interval and chord type recognition exercises don’t really work. I personally found them very convincing.
I’ll check it out. Hopefully I don’t get a bunch of email spam daily like I do from other sites I’ve bought lessons from.
Looks like it’s on sale again for €347 with the code SUMMER23 for the next 4 days.