I've been a user of this add-on for over a year and had been quite satisfied prior to the add-on swapping to a Webextension. This is why I can only rate it 4/5 stars instead of 5/5.
Since Firefox 57, the add-on lost a few key features that I found very helpful. Namely, being able to right-click a link and choose to either "Switch to Reader view" or "Open in Reader view". It's not a big issue, but it adds up to a fair amount of repetitive motions over time in needing to close multiple tabs. This could actually be mitigated a fair amount if the other feature I use to use quite often wasn't taken away: being able to "open in reader view" when right-clicking a link when reader view is already open.
Opening links within Reader View into another Reader View has been removed entirely from the update to Webextensions. This was very helpful in not having to click on the link, wait for the page to load, then open up Reader View separately. This was one of the big selling points in using the Add-on for me initially. I hope this feature is eventually added back.