Why should Rashad be a messenger anyways? I never heard of Rashad Khalifah till recently. His 19 code was made famous by Ahmad Deedat. Anyways everyone should provide evidence from the Quran. I am not sure what is meant by messenger here.
Anyways in the end people should follow those who bring forth evidence from the Quran. Rashad or whoever is not the author of the Quran. Sunnis and Shias must also pledge loyalty to the Quran and abandon this notion that traditions takes precedent over Quran.
There is a lot of people who would manipulate religion for their own purposes so strict observance to the Quran is needed in all situations. This is the straight path.