I know you can force the Reader Mode via About:config, however I like being able to distinguish which pages Firefox "supports" reader mode, vs when it needs to be forced.
The only change I would suggest, I don't know if the addon keeps a state recorded, but I keep finding myself pushing the addon button to try exit reading mode - since I used the button to enter reading mode, only for nothing to happen and I have to click the traditional reading mode button to exit. I know I will probably learn not to do this "wrong behavior", but I would like the addon button to Enter/Exit reading mode, it just seems more intuitive. The button's hover text does say "Toggle Reader View" after all, and not "Turn on Reader View", so I would expect it to actually toggle :D