Thanks for your quick reply. I get the feeling it *might* work if each of the four PBPs are effectively treated as independent monitors with completely separate inputs but as you say, it's not officially supported and I would have no other use for this screen if it doesn't work (other than try and persuade a Window-using colleague.to buy it off me!). I think I'll look at Dell's 24 or 27" ranges and get one of those 4-monitor desk brackets.
Incidentally, the KM switch I use switches keyboard & mouse only, it doesn't switch screens. So I can work on two PCs, look at 4 screens but use just one keyboard & mouse.