For me, it was how amazing Sync's navigation was. I found myself trying to use Sync's gestures in other apps--they're THAT intuitive and reliable. I'm honestly surprised Google or Apple haven't poached the developer to work on making the UIs of their built-in apps work more consistently.
For now wefwef is really good and does everything I need this type of app to do (mainly adjustable font sizes for my old man eyes with a minimalist interface which I prefer over the information overload that most seem to prefer, different strokes and all).
Whoa, Sync has been my most used Android app for the past 5 or 6 years and I never knew the origins of its name. I just figured naming products is harder than most people think (trying to be original and memorable) hence the basic Sync moniker.