Only thing I can think of is you do not have control of the reservation. If you want to put in room requests or that type of thing you have to call the agent and they contact Disney. Though I don't consider that a disadvantage exactly, just a difference in doing it yourself and using an agent.
That doesn't bother me. Can you cancel 5 days prior like with other room only reservations? The email says you can.
Does anyone know what SV at Poly would be like? Better than other SV options at like YC or BC?