Went to the Pool Store to talk about closing, and they were selling a Closing Kit that contains two bottles: MetalFree and PhosFree. The idea seems to be to remove phosphates and deactivate metals to prevent stains.

Any thoughts on this?

Unless you have metals you don't need it. And even if you do there's better stuff out there.
Close properly according to pool school and you won't need any of that stuff.