G'day @Tajipat80, Are you asking whether you'd still be able to stream Netflix data free whilst casting?
The must mentions for this offer states the following:
Mobile TV streaming is suitable for one stream per service on mobile and tablet devices only. Mobile TV will be streamed up to 1.5Mbps in SD quality.
You'd need to ensure that you're streaming in standard definition if you cross into 72p territory then you'll definitely be charged.