In addition to what @ww wrote, there is a key point when adding the MPLS circuit, as you intend to. By bringing the MPLS circuit into the Layer 3 core too, whether via a firewall or not (depending on your security requirements), you’ll provide a path to the internet from the MPLS network, which is required for the AutoVPN to work over the MPLS network. And the tunnels that form over the MPLS will also be able to reach the one arm concentrator.