Doesn't work at all. Install, click +, nothing happens.

It seems to work on most websites, which is definitely a bonus for the addon. Unfortunately when you start it by clicking +, a bulky, big page scroller appears on the page on top of the article you're trying to read. So then you always have to move it out of the way first. It doesn't really have any value besides being in the way, since one could toggle the speed a lot more comfortably without it ever appearing.

There are only 5 levels of speed, and you can't customize your speed beyond this, so if your reading pace does not match one of the set speed levels, you will find yourself clicking down/up manually on the page to keep up with where you're reading. I use the arrow keys to do this, which I discovered, disables the pagescroller. So I at least have to do a fair amount of toggling while trying to read articles with the addon, which is a pity since it's supposed to be a hands-free addon.

Long story short, plus from working on all the websites that I tried, minus for bulkyness and non-customizable speed, both of which result in it not being userfriendly.