Thanks R. Yes of course, understood re research, but I have indeed done some; 1) Amazon products, 2) my local Apple shop and 3) Logitech themselves; before coming here.
The C920 was chosen after considering the first two sources. I expected them to be reliable.
So coming to this forum wasn't my first call at all. I chose a Logitech C920, only subsequently to be told by Logitech themselves that my OS 10.15.2 Catalina is not compatible, so was caught out. I sent it back.
In all the three reviews you cite, Logitech figure prominently and yet the Logitech lady this morning tells me on the phone that they do not supply any web cam product compatible with my system. This, despite "OS 10.10 and subsequent...." being the criterion for compatibility quoted by all product descriptions, including Amazon.
So, I wondered if anyone else on this forum has had this issue. I thought this was what the forum was for.