@mc1392 the Time Series Visual Builder is currently marked as experimental because we plan on rolling similar functionality into a consolidated visual editor for an improved user experience. If you'd like to follow the progress of this project, please subscribe to https://github.com/elastic/kibana/issues/17076
That being said, we test the Time Series Visual Builder as we would any GA visualization. The same is said for both the Input Controls and Vega visualizations. For TSVB specifically, a lot of our users use this visualization type in production and product-wise, we ship visualizations created from this UI with our Beats module dashboards out of the box. It has been in the experimental stage since 5.4 and we've decided to leave it with this flag until we introduce this new editor.
I hope this provides enough detail and context but please feel free to ping me with any other questions. @timroes may be able to provide some additional information as well.