(updated review)

It's great. It's very adjustable and the sound is pretty transparent. It activates automatically and reliably, unlike many other sound boosting addons (that either don't self activate reliably or have to be manually activated every time). It also doesn't mess up Youtube's playback speed options, they work correctly, also unlike other volume boosting addons. It doesn't work on every site under the sun, but works for many major streaming and music sites.

The only problem is that there are some audio stutters (especially on Youtube). They don't happen often, but kinda annoying. In it's defense, this is a problem that other volume boosting addons also have, so maybe there's just no way to have it working perfectly.