They also have to return a retrieved statement from each account (per reg)
Demonstrable consent is required and this is one way to do that. But there are others. And if it works for one account, it is logical to assume that other accounts will have the same result so one time should do you if they want to add accounts later.
I agree that it is best on an account by account basis. You may a one person who is joint with several others on several accounts. Each of them may not want e-statements, providing this "choice" as a good alternative.