Why are you suggesting software you don't even know the feature set of? Your second statement is factually incorrect.
Yes, I use Readability. What does "preferred font" mean to you? The aforementioned software allows for a fixed set of fonts that correspond to color themes.
I genuinely believe this is off-topic; or better yet, it is a "rabbit hole," if you will. I prefer the idea of using Stylish on the Website itself. (And so bear in mind that we're already talking about a 2-degree override. Not to mention becoming dependent on Readability.)