For species with low humidity requirements the spray on type may work but will likely cost more. Even if the cost were the same, the brush on water-based Polycrylic is very easy to use. You can really slop this stuff on and it will level out nicely while it dries.
For species that scratch a lot and/or need some humidity the spray on stuff will flat not work (neither will the water-based). At least as far as the self-propelled spray can products. I'm sure some of the super expensive sprayers can apply the oil-based polyurethanes.