I did ESA East last year. It was a 2 day group lesson, I had Tom Burch, a fantastic full Cert (LIII) Instructor. I then later spent a full day with him alone in Colorado. I wouldn't say that the ESA East was equivelant to 20 lessons though, it was basically 2 lessons, since he had 5 or 6 of us to split his attention to, I figure I had about 3 hours of his attention on that weekend. He however had that amazing eye that could see just what I needed to work on (in my case ankle flex was a big one.)
In the last 2 weeks, I've had 2 merely 1 hour lessons with a LII at Wachusett. Same thing, it's the eye (and he has only one, wears a patch over the other)
that is the thing. He immediately identified the areas I need to work on.
On a humourous note, the one eye caused a bit of a problem when I decided to pass him on the right (his blind eye side) and he made a big sweeping turn across the hill and we crashed! I went down. He asked me if I needed a couple of minutes, I answered "I'm fine. I think I'll need a couple of minutes to see if I need a couple of minutes."