I’ve been chopping and changing back and forth between the old course and the new recently, doing a bit of revision.( I originally finished the new course almost a year ago.)
There are some things that I have found the old course quite good for - drumming home certain rules and constructions. But my goodness, I think it shows up , through contrast, how effective the spaced repetition technique that Aran and co perfected with the new course is.
Even though it has been months since I last did the new course, I found I could still do the last lessons of levels 2 & 3 relatively easily. The last lesson of old course three, though, is an absolute killer!