No. It doesn’t stop the users on your account from charging other items to the bill. Examples s include calling premium rate and international numbers, sending picture messages, entering competitions and making charity donations.
Opting your additional lines into My Account Controls means that any caps or bars you set, or even those you have set in the past, can’t be changed by the user of the additional line.
We recommend you review the caps and bars you’ve applied after opting in. You can do this through your online account under Services and extras.