I actually work in health insurance so hopefully I can help.
"Allied with Aetna" usually does mean you'd be enrolling into an Aetna policy. In some states, you can get health insurance without a specific plan sponsor, aka, from your job. Thus, you'd get the options you're currently choosing and those options could be aligned to a specific health insurance carrier, which is better since the policy is more controlled, over getting insurance without a health insurance like Aetna backing it.
RBP can also get iffy since each provider could have a different negotiation rate, but with an allied health insurance plan like the Aetna one, you'll see a consistent pricing based on contractual rates with the health insurance. With RBP, you could be paying different prices each time, higher or lower, and that $13 less that it is now, could be increased or decreased based on the provider you see. So, that's something to keep in mind with places that negotiate pricing.
Personally, I say go with the allied plan with a health insurance, but always double check with your provider since they can call and also be told if that's included in their contract (I know you said they're closed, just saying for the future).
Hope this helps!