As far as I can tell, since it only uses the player for getting the surface, it shouldn't need to iterate through the players and should work in multiplayer (though I haven't tested this). It might stop healing (temporarily) while you're in a Factorissimo building however since that changes your surface, and very likely does strange things if there's more than one force of players on the map. I'll try to fix it up later today to work with multiple surfaces and forces.