Interesting views.
I instruct at a school which regularly instructs conversions.
I would NOT recommend conversions.
The good pilots can do it 3-4 hours, however, I have seen more problems with the JAA Commercial from conversions than full courses. (In fact every student I have ever seen referred to a CAA staff examiner, after failing at least twice, has been a FAA> JAA conversion.)
The majority of students would be better just enrolling in a full course.
(Cheaper as a package than per hour)