I had one!
It gives you a feeling you are Michelin's mascotte, but I guess that's what an impact vest does, so you are probably used to this feeling.
But since you use seat harness, SB (spreader bar) hight could be a problem for you, since seat harensses has it located in belly button hight or lower, while Cabrinha's imp. vest has it on same hight as other waist haresses, but it doesen't get pulled up so much though. However your center of pull is higher. So a thing to get used to.
It helps keeping you warm.
IT IS NOT A FLOTATION DEVICE. It won't give you any aditional buoyancy, it has additional drag when body draging.
I hate, there is no quick way to fasten the SB other than straping it in every single time unless you put it on through your head like a sweater. It's a pain on freezing winter conditions when you don't feel your fingers and you have to insert the straps trough 4 holes, to tighten the SB.
If you also land/snow kite, it is a pain in the a**, because you can not put it over so many clothing layers (similar with waist harness) and you have to have a big jacket to wear it over it, zipped only at the bottom, up to SB.
I would recomend you trie it before you buy it, if you have a chance.
If you can get used to higher SB and the fact you must get used to straping it in to get it quick and you would use it only for water, this is def. a good harness.
I switched to Ozones Access SB harness. Now that is freedom.