Just make absolutely sure it does not have a "both" setting because then you risk saltwater backflowing into and contaminating your freshwater system. A or B only type of valve.
Also, two separate On-Off valves as seen in an earlier illustration could cause a backflow situation if someone opens both valves at the same time....bad idea.
Be careful with buying
brass valves at home centers. Saltwater corrodes through brass relatively quickly. You want silicon-bronze valves for saltwater if you are going to be using metal over plastic valves.