They definitely eat something other than veggie cakes after taming. I know this because mine haven't starved. Trough has berries, raw meat, and spoiled meat in it so I'm not sure which is being eaten. Definitely worth the effort if you have trouble getting cp.
if you want a lot of cementing paste but don't have veggie cakes, call up your argeventis and swing by the swamp. use the argy to pick up a wild achatina and carry it home. drop it into an enclosure and boom! free paste, no taming required. just make sure nothing gets in and kills it
They worth the veggie cake. It gives 100 paste and organic polymer. Just level up their food so they won't be hungry fast.
I have 2 bee hives and 7 tree sap taps (important to make veggie cakes). I can produce more cakes than what my 2 achatina can consume at a time. Now, I never run out of paste and have a lot of veggie cakes (I needed separate refrigerator just for my cakes)