The other difference between PFA and certified is time. A licensed engineer is working against the clock and is primarily interested in getting the job done safely in an affordable amount of time. Some PFA aircraft are maintained to very high standards because the owner/builder is happy to spend 10 hours polishing, checking and perfecting for every hour flown. Such an owner may well construct most of the parts used, often from very high-grade material, and to exceptional tolerance. If you compare such an aircraft with a public cat club aircraft you will see what I mean!
This is not to say the PFA world is perfect, far from it, but the best is very very good indeed.
Rod
(kit aircraft ordered but not yet arrived)