I think that a bladder press does a better job of distributing the pressure over the grapes. They are much more expensive and I do have at least one major fear.
The grapes I get come in crates held together by nails. I always figure that there is a chance of a puncture. I believe that some bladder presses work under air pressure, and others use water. If a pucture does occur, then I think that one needs to purchase a replacement. If using water, there is a chance of water ending up in your must.
I do have a friend that swears by his bladder press, but I am more comfortable sticking with my hydrolic plunger press.