They make achatina paste till they have one stack(100) and then begin producing organic polymer as long as the paste remains. They also increase the spoil time of organic polymer when in their inventory. Be sure to have plenty of cakes or they will starve. You can still get a lot of paste before they die though so not a complete waste if you cannot continue feeding. Only tame low level achatina.
If you want to tame it on a swap, but you're afraid that you will get sneak attacked by any of the 3 horseman of the swamp, just kidnap it with a preta and land it near your base, then you tame it without many troubles.
If you are considering breeding these, go slam your hand in a car door a few times. It will be much less painful. Literally one veggie cake per percent of growth....and it grows slow.. Digests roughly one point of food per second, so feed a cake about one for every 7 mins (during event boost) and it will gain one percent of growth.