I did it on and off for a few months. It made a lot of sense. However, I didn't really lose on it, maybe a few lb max. I found it quite stressful having to think constantly about whether I was hungry. Sometimes life gets in the way and you can't eat what you fancy and take time over it. And I think he underestimated how much some of us have screwed with our appetites, sugar addictions etc over the years. or how issues like hormone problems can make us crave bad things. Also we aren't living on a natural environment but are bombarded with advertising with fatty, sugar food easily available. And if you don't learn how to make healthy versions of food, as SW encourages,how can you ever choose to want them?
The main time it helped me was on holiday when I ate delicious Mediterranean food, enjoyed it, and realised I was too full for pudding.
Mckenna is very anti diet and would thoroughly disapprove of combining his method with SW. But I think it could work well. You're re educating your body out of old bad habits and tastes, while at the same time preparing for a more confident relationship with food lifelong. With SW there can be a tendency to just inhale all the free food, and it helps you stop and think and fully enjoy it.