If it works for you thats fine.
But its naughty to imply that your minutes are for all providers.
Its the same as trying to work out roaming coverage and cost, the devil is in the detail.
As above ive been using giff gaff for years. They have recently updated there usage and it also covers tethering now.
You will probably find your bundles will change over time. Just worth reviewing now and then.
What boils my blood is the incentives for new sign ups and a loyal customer ends up with the worst deal, because they think they are being looked after for being loyal. Not so....