I understand you about the security, it is really up to you, but naturally they do roost, so that is why we install roosts.
It does lift them up off a cold floor, in winter, and also keep them away from any bugs and nuisance that may be on the floor.
You are right they are perfectly secure in your set up.
When birds are kept in large buildings, and you buy them as POL they have not been able to roost more often they are kept in cages, so they do not know how to roost. In the wild they would learn from other birds.
if you only have 2 then you are their teacher. It also ensures that you can put a poop tray under the roost and save on the mess they make.