Alan, its inflatable, which is great because we can fit them in the backseat of our truck when we have our camper on. We have an electric pump to inflate.
Ben, when the water is still like this they are really quite stable. My wife has never fallen in, but she gets down on her knees more than I do. My first day I went in 3 times, but it was rough water, with a lot of boat wakes, and a hot day, so I didn't mind the swim. I've fallen in twice since then when the fins on the back got caught on underwater log/branches. Both times I saw them pass under me, but was too slow to get down. If I stay out more from shore I don't think I'll fall in any more (we don't go when the water is very rough).