Not having used Manjaro personally, what's the advantage here? My impression was that it was essentially Arch with a user friendly installer and possibly some nicer defaults.

This seems desirable if you're setting up a PC, but is there really added value there if you're building a ROM image for a phone? It seems like you'd be doing a ton of manual installing and configuring anyway, since it's such an unusual target compared to a typical desktop, regardless of cpu architecture...