What's the best solution to make sure xenforo pages are readable on smartphones and pads/tablet? Tapatalk? Is there something else? This should probably be a xenforo feature in the future, if it's not already available.
The mobile style is an optional style - your members would have to select it manually on their mobile devices.
I'm not sure if the Tapatalk and Forumrunner add-ons will both work on your site together, or whether you'd need just one or the other? There are separate threads going for each plugin - I'm sure someone will be able to answer on those threads.