Does anyone know if the V11r maintains its water resistance with the optional metal switch?
Yes, it does. The metal switch assembly is basically just a metal cap. Underneath is a waterproof rubber cap for waterproofness.
That said, the metal cap is GARBAGE! It's one case where Sunwayman went with form over function. It looks pretty, but it constantly binds and grabs the surrounding metal. It doesn't function well at all. There were so many complaints about it, Sunwayman eventually started shipping replacement button kits with the old-style all rubber buttons. The old-style switch looks ugly but works much, MUCH better.
My advice: Only use the metal tailcap if your light's only purpose is going to be to sit on a display shelf and never be used.
