The problem with those techniques vs the marching through the SM is that you need a visible light source on screen / occluders on screen to get proper light shafts.
Using the shadow map information means they will be correct regardless of where the light source and occluders are. Your main issue becomes dealing with occluders which are not in the sm range. You can also use the ray marching pass to compute atmospheric scattering, which is a nice added bonus.