RG35XX Plus vs RG35XX SP (what does the “Plus” mean?)

I’m interested in the RG35XX SP for pocket-ability reasons but the photos of the RG35XX Plus make it seem like the screen is better.

When I look at the specs, I see they both have a 3.5 inch screen with the same resolution.

Am missing something?

Which device do you prefer?

Lastly, how badass would it be if they made an aluminum version of the SP?