@kbdb79 

The M9 has a VPN passthrough, meaning any of your client devices that run a VPN will not be blocked by the Deco so no additional configurations would be needed.

A VPN will help keep your activities private so if someone gets on your network, they won't be able to cipher the packets being sent from your VPN to the internet. 

If you use various public hotspots or hotels, having a VPN your phone or computer uses would be recommended.

With respect to your home network, my worry would be that in using a VPN it is additional overhead so it will affect your speed. Having the Avast I think should be good enough, but if you would be at more peace of mind, then go with the VPN. It could be the speed won't both you for what you use it for.

To clarify, if your laptop say used a VPN connection, only that laptop would be slow, the rest of the devices not on the VPN wouldn't be affected.

@kbdb79