So, if you can make tagines using a dutch oven, a large soup pot, cazuela, casserole, etc.. What exactly are the benefits of cooking in an actualy tagine vessel?
The conical lid stays cool during cooking, moisture from the ingredients that are cooking condense inside the lid and drips back down, which in effect is a kind of self-basting mechanism.
I think it's easier for beginner cooks to prepare certain kinds of tagines in an actual tagine vessel for several reasons. The meats or poultry do not have to be browned first and there is less to fuss with in terms of fiddling with different temperatures during the cooking process.
Certainly, clay or flameware tagine cooking takes longer than a pressure cooker, but only a tiny bit of that time is actually spent working on the dish.
You can layer your meats on the bottom and vegetables on top, and leave the whole thing to slow cook while you read or play with your kids on a weekend. When the tagine is done, you will have a rich, thick sauce as if by magic. This is the beauty of tagine vessel cooking.
Tagines that are essentially pot roasts with larger cuts of meat and bigger pieces of vegetables tend to benefit the most from cooking in a tagine vessel. A quick cooking tagine like my seafood tagine can be cooked in any pot large enough to hold all the ingredients.