I have the Onyx auto/manual. Matter of fact I bought my whole family these. We all love them and they are very comfortable. I guess the only pain in the butt with them is having a few extra CO2 charges. Once that vest hits the water in auto mode, that CO2 is spent. Otherwise, you do feel cooler than most PFD's.
EDIT:
I guess the 1 draw back is that when it does automatically inflate, that's it, it's inflated until you take it off to deflate. I guess getting back on the yak to fish longer may not be in the cards.