Just to update on this.. I ordered a Powis Parker Fastback 20, and so far I am very happy with it.
It had a minor fault on delivery which was quickly rectified by the supplier. Once warmed up it binds documents in seconds. Less fiddly than wire binding. Non-technical colleagues are very happy with it, as it seems to be idiot proof.
Occasionally the alignment of some of the spines might be out by about a millimetre or so, but no issue for us to trim that off the top or bottom. Also it was about 1500 EUR less than the prices typically listed online for it.
Ordering some of the other bits and pieces to try out hard covers and printed covers and will see how that goes. Then after that, next acquisition is a gold font stamping press.