Something else occurred to me, which may add several layers of complexity. It may be that some apps individually play nice with El Cap, but don't play nice with one another - or even two or three others in a bunch. That would make it nearly impossible for normal civilians to sort out, and would account for some of the bugs in the first or second iterations of the software we get.
Re the RoaringApps site: the guy has done a very helpful piece of work, but, as he says, he didn't do all that testing himself. He relies on reports, which may or may not be reliable or up-to-date. That means that the verdict on the list is probably a good guide, but may not be accepted blindly; checking the apps individually lets you know how many reports he's gathered, and the more reports the more reliable the assessment. Case in point, the faulty Kensington driver I found. It turns out that his report of this was a bit misleading (but not his fault), because it was based on a user's experience with it on an earlier OS - which I only found out just now; I, too, know it worked fine back then. So the more research you do on his site, the more you know how to proceed.
