When you set keyboard focus on a UMG button and use a game pad to navigate the menus, you get a nasty looking focus ring.
It can be removed using a C++ class override and modifying the DefaultEngine.ini - but what a pain.
It would be so much easier to just have an option in the UMG blueprint “Disable (or Hide) Button Focus Ring” for when the developer provide his/her own focus visual. Additionally, it would be ideal to provide the ability to style it as desired.