The right model depends on ownership
Dedicated developers work best when you need sustained velocity and product context. Staff augmentation works best when your internal team already has direction and needs specific execution capacity.
Decision criteria
Look at roadmap clarity, technical leadership, communication load, release frequency, and how much product ownership you want the partner to carry.
What to avoid
Do not choose a model only by hourly rate. Poor coordination, unclear acceptance criteria, and weak QA can make cheap delivery expensive very quickly.