I generally recommend to persons wanting to tether that they buy the cheaper £20 Goodybag, as it not only doesn’t drop to unusable daytime speeds after 80GB used (but, after three bags purchased, gives extra 1GB full speed), but also is not subject to ‘Traffic Flow Policy’ which can also slow things down if a large amount of data seems to be being used in a short amount of time.
Tethering was always prohibited on ‘Unlimited’ Goodybags; now it is allowed as the bundle is NOT unlimited data, but at many times not really possible if data is slowed.
For those who want to use off-peak data (between midnight and 8am), it is possible to re-start your device to speed up your data flow at midnight. Some do just that, and manage to use a lot more data than most others, but at a time that doesn’t adversely affect most other users.
A bit like the Economy7 Goodybag I once suggested, you are able to use data while others sleep. 🤡