App layout library

Wondering if the layout render will be smart enough to avoid flicker

It's able to clear just the area that changed and then render the text. It's what most people do and mostly avoids flicker. I guess usage of offscreen buffers could be an option but the idea of this is to be lightweight - not to grow into an all-encompassing UI library.

layout manager is not the only option

No, you can do whatever you want.

eg a rotating arrow for a compass

That's why we have the 'custom' element - so you can render just the bit that you need, but where it is gets handled for you.