I've used this for over a year on a large forum with over 20 million posts. It's been working with no problems. Honestly my benchmarking isn't good enough to exactly how much this improved things, but it didn't break anything either.
Same addition as this https://xenforo.com/community/resources/optimized-list-queries-by-xon.6869/. Also, if the developer would look towards the predis or phpreact library, where there is completely asynchronous caching. It would be much more interesting to watch this. This supplement is what is missing from the box and should be required. Specifically, in the current version, the set of features is very scarce.
We've been dealing with some serious server load issues since upgrading from XF 1.5 to XF 2.1. Out of ideas, we decided to give this a shot. I'm not exaggerating when I say our CPU usage went from near 50% to the 20's. If you're not running this, you should be.
As long as you meet the Redis pre req. its changes the already fast instance of Xenforo2.1 to lightening quick. It really is like greased lightening with this addon. Thanks very much for your work - TurboRenault.co.uk