I've just bought that cheapie keyboard case, and the top prong is now adjustable. Admittedly I also put it in a gel case when it's in the keyboard case, for added security, but even without it, I think it would clamp down and hang on for dear life. A friend of mine also bought this case the other week, and reports the same thing. Hers is the basic black model, mine is blue, but I think they're all the same. It's a nice blue, incidentally. I don't know how robust that adjustable prong is, that said, and I can't see it lasting forever.
If you do need to find some method to keep the tablet in the case, a lot of people have been using self-adhesive velcro, sometimes attached to a gel skin instead of the original tablet. If I ever start to worry that mine won't be secure enough, I'll spend a pound on some velcro.
Typing is harder than I expected, however, and I say this as a woman of 4'11" with accordingly small hands. It's partly the key spacing and partly the occasional oddities in the layout, such as the position of the apostrophe key. But then I gather that the bluetooth keyboards tend to have similar problems. I bought it for occasional use, and ironically I think I'll have to practice before that's really feasible. At least, if I want to use it for taking notes somewhere without making a mistake in every other word. But I'm fairly close to that stage already, so I don't think it'll be too hard. It just means that I won't be able to ask someone else to take notes for me.
The other thing which is slightly annoying is that the USB adaptor sticks out at the side. I did at least work out where to store it safely when the case is folded up: unplug it from the tablet and put it so that it's resting just above the top of the tablet. You'll have the thinner cable trailing over the screen, but I can't see that this would cause any problems. It does at least mean that the cable is safely tucked away and not likely to fall out or get damaged in transit.