I replaced some old Thule Prorides with Highroads, partly because you don’t have to faff to put them on the other side of the car, back to front, etc and partly for the strap attachment. The T track thing always bothered me because it whistles so if I was using the racks without cycle carriers I’d have to put the rubber insert in.
The strap attachments seem very good, I’d just use those if I were you. They have a steel band and the cover can be locked so they are secure against opportunistic thievery.
Edit: Just looked at the adaptors. I’d say they stay attached to the rack, you then slide the whole lot onto the bars. Probably need to be tightened once in place, which I’d guess that thing that looks like a stud key is for.
