It's interesting how far this has drifted from the original question: which was about PPLs managing to take proper command of an aeroplane. That said, the subsequent discussion has been incredibly informative and I hope that everybody else has enjoyed it as much as me.
I'm planning to do a CRI course sometime in the next year - which I was planning to do to scratch a personal itch, but will hopefully benefit the two syndicates that I belong to. I've also, incidentally, been trying for some time to persuade the (rest of the) syndicate on the more difficult aeroplane that we should give a "known good" local instructor some regular hours on the aeroplane so that they can maintain recency and be useful to us - I think that I've finally just about won that argument and have arranged to check him out next month (the instructor and I used to share an even more interesting aeroplane, so I trust him).
It's also a really good idea to have a clear "checkout procedure" existing within the syndicate and I'm going to try and pull that together with the other most experienced pilot on type. I think that what I described earlier covers the shape of that - but obviously covering syndicate, airfield and aeroplane specific stuff as well.
I've also had clarified usefully in my mind that there has to be a point where I tell somebody that they really need to go and spend some quality time with a proper instructor (depending upon my spare time and patience, and how poor somebody's piloting and airmanship seem to be, that may well remain the case after I've done a CRI !).
I think that about covers it?
G