I picked up the Poseidon from REI and took it out on the water over the weekend. The reason I got it was that there is a hydration sleeve on the back and loads of options for carrying items. I like the thought of, if it is not on you, then you don't have it. So with the ability to add additional pockets and accessories, I think this will really work for me.
I'm 6'4" and about 250 so the XL/XXL fit great and there is enough room to layer underneath. The fit is excellent and very comfortable. I even forgot I was wearing it.
The drawback is with the hydration sleeve. I can fit a 100fl oz camelbak reservoir there and the bottom hangs out slightly. No big deal, I just nee a smaller reservoir. The other item is the velcro loop the reservoir hooks to. It is too weak for 100fl.oz of water. So I ended up adding some nylon cord that attaches to the straps of the PFD to allow for more support. Overall, I'm really pleased and can't wait to get out on the water more. Hope this is helpful.