These are definitely a great addition to any tablet if you game regularly, as they make movement so much easier, they are a god send to someone like me. They work with almost any game really, aslong as the D-pad area isn't fixed too close to the edgemof the screen (most games have a floaty one which will sort of centre where you first touch the screen, which works wonders with these). They are actually surprisingly accurate too. Playing something like the recommended Super Mega Worm, you can easily pull off small circles, and it will follow every small movement, a hard task to be able to pull off with just your thumb.
They are not without fault though, as they have a tendancy to move a little, and after a while the suction cups can come off, but if you clean the screen and the cup they usually last a good bit longer.
For the price I highly recommend these. They aren't expensive, and they help immensely. You'll be surprised how well they work, considering they still interact with the screen.