Thanks. I red it twice and didn't see it somehow... ;p
So basically it looks like we should switch to Prime first, make sure if it's working and then install optimus-manager.
I kinda hoped that it would magically set all things correctly with mhwd since it's in Manjaro repos but I suspected that it won't be the case, so I had to be sure. So installing on bumblebee would rather cause conflicts and make system unbootable.
I wish that mhwd introduced support for this package or even integrated it so it would be capable of switching between bumblebee and prime with switcher automatically.
EDIT: @philm, can you consider integrating mhwd with optimus-manager so we could finally choose between bumblebee and switchable prime in an automated way? Too many people are messing with gpu drivers and wasting their systems and ubuntu-land newcomers expect to have something like that, which isn't a bad idea considering that Steam Play needs vulkan while bumblebee doesn't support it.