@jay_b the lack of VIP will affect how your users are seen to other sites on the internet, so if a 3rd party gives you access to a service via your public IP you'll have to give them both IPs, which some don't accept...
If you put the same IP on WAN2 of both MXs the dashboard will allow it, but you will get 50% packet loss. I know as I accidentally did it when testing something yesterday... 🤦♂️