Beta drivers are as secure as all the other WHQL drivers, the testing is nearly the same inside Nvidia. The ONLY thing is, that the Beta drivers are not certified by Mircrosoft, so they HAVE to write this License (or whatever) down there.
The benefit for Nvidia for doing this is to release new fixes quicker.
That's how it is, nothing special or fency

Beta drivers are BETA. These are on testing, and you help with them (you can info them about issues). I remember when Dragon Age 2 goes released. I downloaded the beta drivers, them, cause dx11 was working weird...
The driver solved the problem, but at certain point, part of the screen become black., at random. Then you had to deactivate dx11 to run the game, or restart this.
Beta drivers are beta. If you want, you can use them. But the possible problems you have with the game, they does not need to be caused by the game.
Anyway... One month and no dx11... -_-b