More Info: https://xenforo.com/community/threads/optimized-list-queries-by-xon.103106/page-4#post-1114877 Optimized List Queries by Xon Does this work in 1.3? It should, but I can't offer support for it. xenforo.com What value should I put into Controller for it to work fine?
Where are you using the online user widget? If you use it on the index page, it should already use the existing data available and does not query new data by itself.
Regarding this issue, I think using template + controller callback is a waste since the controller action will do a bunch of stuff which will outweight the saving made by optimized query. The best way to do it is to have an optimized widget built by Xon and bundled in his add-on IMHO.