Pre-cooked shrimp are unfailingly pre-overcooked-shrimp, and are impossible to add flavor to the way you can with raw shrimp. Shrimp that are raw but peeled and deveined are a small step up, but often get mangled and beat up in the cleaning. You are much better off buying whole, headless shrimp (or at the very least E-Z peel) and cleaning them yourself. It’s a little more work, but worth the effort. This video will show you everything you need to know.