I hope “bumping” my topic is ok since its been a while and Im updating the information on this item.
I was at ToysRus today and delighted to find a Nerf Rival Atlus, and close by these vests were on available. The Rival vests were a very reasonable 19.99 USD. In fact, non rival nerf vests are on sale for just a few bucks OVER that online. The hit points rely on your opponent to be paying attention to when he gets hit, and he must manually pull up a two-sided yellow/black piece of cloth sown into the upper left part of the chest, and fold it over on one side or the other. Both the black and yellow side have velcro strips at the end, to hold it in place in either position.
I didn’t buy it so I couldn’t tell you if it fits a grown man. For 20 bucks it seems reasonable, provided you have enough people to play games with nearby.