The official demo won't be out until the first of next month.
The beta is all over the place, but it's buggy and missing a lot of basic scripts. It does however contain pretty much the entire dev package as well though. If you are a game modder, you might grab it up just to have those tools down the road when the game is actually released.
Grabbing it up for a chance to play the game would be a real effort and probably quite time consuming too though.
Honestly, if you just want a chance to test it on your system, I would wait for the official demo to be released on the first.