I don’t think that’s entirely correct 
From what I could see in my tests, while it is fast to get a final image (and even faster to get a preview), it is not orders-of-magnitude faster compared to, say, V-Ray. And it will get slower as they add more stuff.
The interactivity of course is unbeatable as the renderer and the application share the same data and general framework.
Best regards,
Vlado