I used the astronomyshed video procedure on my 10" f4 Newt about six months ago, and the result was good. I had a little bit of trouble with his accent and terminology, but after a few iterations, it all came good. I then covered up the f4 and wandered off into widefield stuff and haven't yet revisited it.
IIRC, the key was in using the crosshairs to keep everything lined up, and then verifying results with a reliable laser collimator + Barlow as in his final steps. I have always liked the laser+barlow approach.
Just FYI Peter, in a fit of boredom a couple of weeks ago I ordered a Chinese "OCAL" collimator camera + software (
https://amz.run/53Ym), it's on it's way, so will try that out when it arrives. Wasn't that cheap, but hey, gotta spend it before I go.
YouTube tutorial video:
https://tinyl.io/58UI
My reasoning is that it might make the astronomyshed approach somewhat easier. Happy to loan it to you after I try it.