First off all, I think you want to look at the MB-Lab called add-on. Second, you need the Rigify for MB-Lab add-on for the MB-Lab.
Because the “Meta-Rig for Manuel Bastioni Lab” add-on might not work properly on MB-Lab and has bug, that have been fixed in “Rigify for MB-Lab” add-on.
(I’m just telling, because you might have been confused with the names. You’re not the first one. 
)
If you want to use the face rig from Rigify: You have to do weight paint on your own.
If you want to use the face rig from MB-Lab (bone driven shape keys): You can easily detach the face rig panel and join to the Rigify rig after the generation. That should work without any problem.