There is very good data on hyperhydration and endurance capacity...if i was an endurance athlete I would take GMS before every event. I feel the proven data on hyperhydration is enough to make it worth using, compared to theories floating around on it effecting performance. I actually have never once read a single person say it negatively effected their performance.
Its not going to make you crazy vascular pumped, its more of a full bulging pump. For endurance athletes its a must-have IMO