have owned a patagonia impact vest that i wore under my wetsuit surfing norcen cal reefs that warranted it and now that i live hawaii am the proud owner of a buell rb1 padded springsuit that i wear in similar conditions
the impact vest gave me a lot of confidence surfing larger waves with a big board. it is definitely a little bulky and awkward, but when you're riding a 9'+ gun and wearing a 4/3 etc. it doesnt really matter. I think a lot of wearing it was mental for me -- like doc says it has float, but not a ton -- but it's enough to give you the assurance when you take waves on the head or fall that you're headed back up. it's also enough float to really make swimming if you lose your board much easier.
i can personally attest to the impact protection - i took the fins of my gun to my ribs hard enough to break out the fin box part way and only had a tiny cut -- would have been really bad if i didnt have the vest
like kool-aid said i would not wear it at a beachbreak situation where you are duckdiving or bailing your board a lot. i wore it once at ocean beach and did not like it at all. it will also stretch the sh!t out of your wetsuit but not much to be done about that
i now wear the buell in similar warm water conditions and it is rad. less spacesuit feeling than the impact vest but still enough protection. the major difference is no padding in the chest, which the impact vest has and puts your body in a bit of a weird paddling position
i don't think i am interested in waves requiring an inflatable vest