Has anyone sucessfully set one up??? I've been trying to set this up and despite to alll the reviews i've read... its not simple process with BT Home Hub 5.
Google WiFi cannot get an internet connection by being connected into the HH5 WAN port (and i tried the GbE ports). I've read that the HH5 can't operate as modem only.. but i'm not sure if that's the issue.
You can't connect it to the HH5 WAN port, that is for connecting the HH5 to a modem. You need to connect the HH5 LAN port to the wifi WAN port.
The Google Wifi system provides both the router and Wifi functionality, just as your Hub 5 does. The expectation is that the WAN port on the primary Wifi point would be connected to a modem, whereas by connecting to a LAN port on the Hub, you're connecting it to another router.
The 'Supported Google Wifi setups' are shown on the Hardwire Wifi points and other devices page, and as you see there, the majority expect the setup to be "Modem → Primary Wifi point → Mesh Wifi point".
On the same page there is a section "Include a 3rd-party router upstream of the Primary Wifi point" that shows the connectivity as @licquorice explained, but this does warn of possible 'Double NAT' issues.
If you dow have issues one option would be to purchase a modem such as a second hand Openreach (Huawei HG612) modem from the auction site, or something like the Draytek 130.