The differences are as follows:

There is additional machining done to the rim and hub shell to shed weight. If you look at the spokes, the bladed section begins much closer to the rim on the RZero than it does on the R1. This is, again, to shave weight.

The ride of the Zeros should be a little less harsh that the R1 can be. This is based on feedback from QuickStep to Fulcrum. That is why they made the changes and introduced the RZero.

The internals are the same.