I'm sure there are.
However, before advising any clients to opt-out, you really need to knowledgeable about WHY you think they should opt-out, and both you and the client need to be know the disadvantages of opting out.
So I think it boils down to "why" would/should a person opt-out?
It is definitely going to take some work to determine if clients should opt out. My concern is those who might have had lower income in 2020 because of Covid. If their income goes back up in 2021 and they don't qualify for the advance payments, it won't be a fun conversation when we have to tell them they have to pay back $3,000 or more.
Income rising above the phase-outs is a valid concern.
However, in my opinion it would be better to warn those clients about the possibility, and if the client is concerned about a repayment they can put the Advance payments into a savings account.