What readysetawesome said. The XR bumpers design is not quite there yet. They are better than nothing and I hope they continue working on it, but as it is now I'm pretty happy that I got float plates on as well.
Maybe the optimal design would be XR bumpers as a shell (current design) with additional "wear and tear" modular slots - say a tailguard and bottom plate that dips below the rails (so they take the contact before the rails) that you could easily replace as you wear them out.
This is close to what you end up with using the float plates. The forward edge of the float plate act as a tailguard, and the rest dips below the rails in addition to adding a quite thick layer of protection to the battery/controller when you do have that really bad smash.
As for rails, I don't like gouging out (over time) the main frame of a device that is carrying me at speed. The rail protectors are an easy way of avoiding that kind of wear. And you get the additional bonus of having the option to become a total fashion junkie now that there are color options available etc ;)