This tutorial is not as informative, since tons of resources have explained how to properly use UpdateAsync, though it would be good for an beginner to understand how to properly save data. This tutorial also doesn’t explain how to efficiently load data with UpdateAsync, nor tells how it respects “incoming calls”. Instead this tutorial; Stop using SetAsync explains it all, this tutorial for the most part has no point or usefulness except the only thing you did was just re-phrase the old tutorial.
This function will be ran with the first argument being the data that is currently there, you can use that data for comparation, getting data from it… etc.
This is incorrect, the callback will always be called despite if there was no data for that key, it will only be not be called is when UpdateAsync fails.