In terms of protein and CO2 eq, the snails seem comparable if not better than crickets, if I’m reading the data correctly, with .7 kg CO2 eq per kg for the snails (edible meat) vs 1.3 for crickets, and 16g protein vs the crickets 14-20g.
Granted, there may be other factors in play, such as how easy they are the farm as you mention.