I've been looking for similar answers. It seems that it gives you internet across your house but I live in a small place so I don't think I need it. I think the support would be useful and apparently the price you get when you buy broadband is frozen if you have Halo, I hope the prices don't go up much more. If we do have blackouts this winter the EE router would be useful, and that's included with Halo it seems or at least that's what I found on this website https://switchking.co.uk/bt-halo-3-review/ I can't think there's much more information on it though. Would be good to hear from anyone who has it.
The EE router needs to be plugged in to work so if you have a power outage it will be just like your Smarthub and won't work.
It is intended to keep you connected if your broadband or the Smarthub develop a fault, not if there is no power to your property.
The support you are given has limitations. See Terms and Conditions in the following link.
"When can I request a visit from a Home Tech Expert? You can benefit from a free Home Tech Expert visit once in every 12 month period. Charges may apply for any additional visits made at your request".
The Price promise means you will keep the same price after you come out of contract but it still allows BT to increase the annual charge as per the annual percentage increase.
"How does Our Price Promise work? You’ll keep the same monthly price, when your contract ends. This doesn’t include any changes as a result of annual percentage increase in the Consumer Price Index (CPI) rate of inflation plus 3.9%. See bt.com/prices for more information".