I just got one last week. Used it once with thin base layer in ~45 degree water (and 49 degree air). Spent several minutes sitting in the water without feeling cold. Bottom fits like a normal wetsuit. Top is baggy enough to fit some heavier layers underneath. No idea how you can zip and unzip without help. That thing is burly! I wouldn't think you could fit your everyday comp vest over it. I wore a O'Neil Assault vest over it with no problems. So much flotation, getting up out of the water felt strange.
After skiing, my lower half was totally dry. I did have some dampness around my upper chest though. Water must have been sneaking in around my neck.
Hopefully getting back out tomorrow to try it again.
(edit to add that I'm 5'-11", 190 lbs, and went with the XL. According to the size chart, I could squeeze into a L, but glad I didn't go with that)