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 is not good enough to see if this really improved things, but it didn't break anything either.
Must have for large forums. New version has been a huge improvement for large Media Galleries. I have a lot of attachments and recently synced ALL my attachments with media gallery 2.2. I'm still doing some syncing but right now have 21,471 pages.
Here's the different in loading that page with and without the addon:
A great add-on that solves forums issues not only with query performance. But besides this, the ugliness of the developers that causes the XenForo Media Gallery rules. Thanks to this add-on, mysql can completely solve the problem with slow queries, in addition, it is ruled by such a disgrace https://xenforo.com/community/threads/xf-finder-join-index-hints.173114/. If you have an average forum, then you should think about this addition already.