In my eyes there is a high risk if the team can decide which method should be applied. It's the most transparent way to give this decision to the team, but actually there is a high risk, when they don't want to work with agile methods. If your whole organisation works with agile methods and only one team decides something else, then it won't work.
So what is your opinion, should the management decide which methods should be applied, the PO or really the whole team?