Stearns is the manufacturer of SOSPENDERS. Great product. I would suggest that if you do decide to purchase the Strearns product that you go with the model that has the 38 gram CO2 cylinder (unless they now make a larger one). I know that they come with 16g, 24g and 25g but I wouldn't bother with anything smaller 38 grams. If KVRSA is out of the fully automatics take a look on eBay and if you're patient you can find one for a lot less than in the boating stores. I got one for under $70 delivered.
Be sure to get a fully automatic vest. The manually deployed vests are not a good solution for airboating and other recreational activities where there is a risk of being thrown from the boat or in quick sinking situations. Also, keep in mind, in order for your vest to be counted as a life preserver you must be wearing it. In other words, if it's stuffed under the seat it's considered to be the same as not having a PFD and could result in a ticket if you don't have another type of PFD on board.