I've owned N4 and OPX and OPX wins by a long shot. Hardware is good (not great because the glass likes to get shattered). Multirom is indeed a no go but what I did when I had to boot android was: make quick backup of SFOS, restore Android, do what you have to do and restore SFOS. The whole operation takes max. 7 minutes. It's not ideal but it's possible to boot Android in quite short time without the need to flash anything.