The barrel having a smaller gas port does not make it proprietary. No additional pieces or parts vary from the standard. All AR gas ports are different sizes and there is not one "right" or non proprietary size.
That BRT is a great option too apparently, and yes you could use whatever barrel you like. I see nothing wrong with that route.
Of course, I was kidding about that "proprietary" barrel. I guess I should have made that more clear.
Yeah, the BRT looks like a better route than an adjustable gas block (cheaper - like ME) and less likely to get clogged with crud (again, like ME).
Thanks for validating that!