The vanilla oat drink that tastes pleasant in coffee may be noticeably sweet in mashed potatoes. Before opening a carton for dinner, check both flavoring and added sweetness.
For savory cooking, begin with a plain unsweetened product. For baking, follow the recipe's specified type when the liquid plays a structural role. Different drinks contain different amounts of fat, protein, and stabilizers, so they do not always behave identically in a custard or sauce.
Buy a small carton while learning what you like. Keep a note of the brand and variety if one works especially well; remembering only “oat milk” may not reproduce the result. Refrigerate opened cartons according to the label, including those originally sold on an unrefrigerated shelf.
Further reading: King Arthur Baking: non-dairy milk in baking.