I've got a mix of M4 and M5 units but I'd like to add a new main Deco that will act as my router and to deploy the VPN feature.

https://www.tp-link.com/us/support/faq/3642/

I was wondering if you could advise which unit would be best for the VPN, and most likely to get new firmware features in the future. My current models don't seem to be getting the same feature set as other units. 

Thanks