I only used Google version but I would guess that:

Nokia: - Nokia approach requires better lens with low aperture, because shallow DOF is done physically not using algorithm - Refocus on Nokia seems to be super fast, because they just change the picture which is used

Google - can use any lens, as bokeh is just calculated - you can change parameters of bokeh (very shallow DOF or not so much) - it requires a lot of computational power, so it take a lot of time to modify the photo