@topher1kenobe ok, here's the trickiest feedback I'll have for you. The `NOT_EXISTS` condition can be ***extremely*** inefficient. Recently I was debugging some an extremely slow query and found that `meta_query` that was causing the performance problems, specifically the `NOT EXISTS` condition. I refactored logic to make sure the post meta always gets added to all posts upon activation of the plugin. With this in place, the `OR NOT EXISTS` could be removed, and so WP_Query could then do a much more efficient INNER JOIN. How much more efficient? In my case:

Old query: 10.327540 secs
New query: 0.006748 secs

In other words, the new query was 1530× faster!