With your solution they will limit participants if they allow only jr members. But if there si survery there is unlimited participants but only one pick of result per game from one user. That is my oppinion.
nobody ever wants to lose their time on free survey,this is a prediction contest..we want to post as fast as possible..so taking a survey for this contest is not a good thinking,also some country can't participate if there is a survey.so let the OP choose what he need to do