This is an interesting thread - here's a punter perspective, which I hope is helpful.
I am a PPL and don't mind two approaches to the training of procedures by instructors -(a) use approved organisational SOPs - e.g. like OATS who publish a comprehensive company checklist for the PA28 or (b) use the manufacurers POH. Either way, the approach is "right", becuase it is officially proven and consistent.
What I find intensely irritating is an instructor who uses neither. e.g. a few years ago I was checking out on one of the heavier singles and landing on a short field [with a flying club without their own checklist/POH.]
As soon as we touched down [and stayed down], I retracted the flaps. The instructor immediately re-deployed them and gave me a lecture all the way back to the parking area about the evils of "doing your after landing checks on the roll."
Have suffered this running tirade without answering back [I don't think that arguing and taxying mix too well] I shutdown and retrieved the manufacturer's POH from the seat back and pointed out that my procedure was defined by the manufacturer and had nothing to do with after landing checks.
Strangely enough, he had little to say when I asked him where he though that his intervention added value to my learning experience.
I also strongly support the instructors on the forum who expect PPLs to be able to calculate C of G and take off roll - the P in PPL may literally mean private priviliges, but it should also denote a professional attitude to flying.
I hope you don't mind me "lurking" on your forum, I'm not a wannabe, just a guy who loves flying and benefits from the obvious wisdom and experience shared.
Just out of interest, whre do you guys stand on the use of commercially available third party checklists which are not officially approved documents?