I am one of the 'fast trackers' and I did my c&g 6129 level 2 domestic plumbing course whilst still in the military. I found it a huge challenge going self employed straight off this course, but I could not afford to work for free for any length of time.
I was determined to learn the trade though and put in a lot of my own time reading, practising at home and learning the hard way too.
you get idiots through into the trade from both training methods. The person and their attitude to work is much more important than how they are trained in my opinion.