They say this
All you can eat data gives you worry free internet use. Even if you used your phone for every minute of every day you could only use, subject to TrafficSense™, around 1000GB each month. We may use this cap to identify inappropriate use of the service, such as commercial use, which isn't permitted under our terms and conditions.
So they will use traffic sense to check if it's commercial usage.
Private no limit.
The 12GB has been raised to 30GB now for tethering.
It's hard to use 100GB on a phone alone.
If you are using it for private use there's no problem.