Should I buy a non-return valve or a butterfly valve?
That depends on the desired effect. As the name suggests, non-return valves are primarily designed to prevent backflow of media. They operate passively and close automatically when the flow is appropriate. An electric or pneumatic butterfly valve with a drive can also operate automatically, but still switches actively. Depending on the design of your pipes, it may even be worthwhile to use a combination of both valves.
