I haven't used the Please Release Me stuff yet, but I have had to use the Mountain Dew trick twice in a tournament and it did stop the bleeding and both fish survived through the weigh in process. I'm not saying this would be the case every time, and I can't imagine it's good for a fish who needs fresh, clean water to live, but it worked in a pinch.
I've heard great things about Please Release Me, and I should probably be adding that to my shopping list for next season.