There isn’t much advantage to the rails. In theory if you could find bars that can easily be moved to any location on the rails, this would give you flexibility in where to put the bars, but i all the bars i have seen have very specific mounting locations on the rails and cannot be moved around. Maybe some exists, i don’t know.
I am also not sure if there are compatible bars for the cx-9 that mounts without the rails. But if there are some then i don’t think the current rails would add any real advantage unless you can one that can be moved around like i mentioned above.
Funny thing though, as expensive as the mazda rails and bars are, they were still cheaper than the equivalent from thule and yakima when i was shopping around. So i went with the mazda rails and bars.
Also the mazda bars are curved, so not ideal if you are looking to carry large flat items.