Not exactly the best combat mount, slow, stamina isn't the best, a little squishy. But a few high levels of these on base defence are pretty good. Put a few in the inner parts of your base (along with the spiders to slow them down) and the will have your enemies armour being melted in seconds!
Acid spit collects corpses. Maybe bug? Also make sure you bring the saddle into the cave with you, or you will spend many aggravating hours trying to get it to follow you out, as it gets stuck on every little thing.