OK, maybe I'm missing something here but why would you want a breaker in the outlet box? 30A should be a dedicated circuit with protection at the panel, right?

BTW, I got my 50A in-use at the orange store for less than 20 bucks. I never heard of the company but it seems well built.
Has anyone else noticed that HD seems to be carrying a lot more "unusual" brands and less recognizable stuff lately?