(?) "Complete" fixtures include both the Trim Kit and the required Rough-in Valve necessary for installation. The valve is the part that installs in your deck or wall and connects to the hot and cold water lines in your home. A "Trim Kit" is great if you already have the valve and just need the part you see (the trim).
Shower faucet controls with integrated diverter are used when creating a custom shower system. Rather than having a separate 3 setting or 6 setting diverter, you can use a shower control with diverter on face plate. This lets you add body sprays, hand showers, ceiling mount showerheads and more!
