I'm squarely in the "I'll never go back to the old way" camp. I admit that I've tweaked the schedule for some short pieces. I'm not taking a 2-week or even a 1-week break if I feel that I'm only a day or two from finishing a short piece.
Having a section of a piece on a schedule also disciplines me against temptation to do a play-through when I get bogged down with something difficult in the scheduled section.
It's still too early to test the application of the method I'm most excited about - keeping my pop & jazz standards repertoire in good order. I'm in the midst of relearning the first of a dozen or so pieces.
I've followed the system long enough to go through the 2-week break on various pieces and I'm repeatedly blown away by remembering/playing almost as well or even better after the breaks.
I do have some concerns whether I'm following the system correctly and what kind of tweaking I can get away with, so I'm eagerly awaiting that book.