The view from a distance...
... living here where RoSPA has little recognition and the IAM recently gave up and went home

, the view of "Advanced" or Post Test Training is a little jaded from the consumers point of view.
I cant say i'd blame anyone, anywhere for being confused at to what's the best for them.
My 2 cents, for what it's worth;
Roadcraft, the book, is sometimes called the bible of training as it is a very useful tool and will never lead you astray.
However, just like the other bible it is open to interpretation and look how much grief the various interpretations gets Christians into!
I'd suggest getting the book first. Read it as suits you, then get an assessment with a recommended Trainer - one who's been used by another rider who's opinion YOU value.
Take it from there and make your own plan as to the best way forward.
I'm a RoSPA DIP - meaning i'm an approved (by RoSPA) Advanced Trainer.
I've met total planks and absolute riding gods wearing both the RoSPA and the IAM badge.
The badge is just that - a badge, a label.
The "System Of Motorcycle Control" taken from Roadcraft, i.e; the procedural riding technique as preached by RoSPA and the IAM is inflexible text, black and white, in a book.
Its application (meaning how YOU ride your Bike out here in the real world) is what makes the difference between sense and NONsense.

... now i'm waffling / time to shuddup.

There's lots of good sense in this forum and probably more local than me - keep asking questions and you'll get what you need.

~~
Og