It is a fairly minor improvement. I have Redis configured to periodically save content, and on restarting it will restore the contents on start.
Compared to an in-memory table in MySQL which is totally lost on restart, and introduces memory contention for other resources. XF inserts a row for each page view per thread, where as this addon increments a counter per thread.
If you have a distributed MySQL instance, this means you don't need to replicate a MEMORY table for what is used to collect page view counters.
Yes. I also have fsync set to explicitly off (so the OS will do it eventually). The idea is for low overhead persistence of cached data but as the data can be easily regenerated, I don't mind if it is lost.