How do we use BigQuery HLL (HyperLogLog) functions in Looker

Question

I have a quick question on how we can use the BigQuery HLL functions in Looker.

For example, there is a BigQuery table with the following structure Sample BigQuery Table

1. In looker do I need to define this field respondents_hll as a dimension or measure?
2. If I use it as a measure, how can I extract the value of this HLL field at a different grouping level(for example, country only) and use it in dashboards without losing its meaning?
3. If I bring this in as a Dimension, I still want to be able to show the extract of this HLL field at different level? How will looker understand the grouping?

Best Regards, Sam