Once you've capsized and swamped, it would seem a little bit late to try to inflate the sponsons for stability. Bulkheads and airbags would do a lot more for floating the kayak higher and reducing the amount of water you have to bail. A properly outfitted kayak (with airbags and bulkheads) should float wih the coaming above the water with the paddler on board. I dont think external floatation devices are going to do much more than an internal air bag and are just more likely to grab a wave, get damaged -- or lock you upside down and keep you from rolling.

If it is stability you are looking for, most kayaks come equipped with a sponson-like device that, when used properly, is much more efficient than the inflatable bags in the picture. You can extend this device out from the boat to increase its leverage, and it can be made to match the esthetics of your kayak. What's more, unlike an inflatable sponson, this device can be used to provide a positive righting force even when your kayak is completely upside down.

You're holding it in your hands.