Is anyone working on Leviton Vizia RF +?

You should ask any questions about using the tweaker in the author thread for that code. That will get you the fastest and most accurate answer.

But the short answer is that it’s not a smartapp: it’s a device type handler. So to use it, you select the device in your “things” list that you assigned to it and then you will be able to set the parameters for that device. But again, ask any follow-up questions in the tweaker thread.