BigQuery GA4 transfer service first impressions

The transfer service has some significant limitations:

• Lack of Join Keys:
  Reports generate summary data, so there are no join keys to add detail. For instance:
  • The userAcquisition table includes a summary conversions column.
  • The conversions table provides details on individual conversions, however, there’s no way to link the two to break down conversions by traffic source.
    
• No Secondary Dimensions:
  The service doesn’t support secondary dimensions. For example, if you want to analyze page metrics by device type, the data structure won’t support it.
  
• Missing User Metrics:
  Total and Active user metrics are not included. This omission is likely because the transfer is a daily snapshot, while calculating users requires a unique count of user IDs over a period. Summing daily active users over a longer time period will produce inflated numbers since some users will be counted multiple times. Personally, I would have preferred if Google included them anyway, but I understand the choice.
  
• Inconsistent User-Derived Metrics:
  Some user-related metrics are included. For instance, the pagesAndScreens view provides:
  • screen_page_views_per_user
  • user_engagement_duration (appears to be a total number of engaged seconds, but without session or user metrics to use as a denominator in metric calculation, it’s not very useful).

Below are the fields that are included in the pagesAndScreens table:

• No event detail
  The event_count and conversions columns in reports provide summary counts of all events. Note that the events and conversions tables do provide counts by event_name, but per above they can’t be joined to other tables.
• Empty Demographic Data:
  In my test, the demographicDetails table was empty. This means no geographic data.