For us what would be most useful would be a way to limit the downloads directly, rather than using a limited reward to restrict access. I think it would be much clearer if the buy button for the game explicitly showed the limit and the number remaining - something like:
Buy now ($10) - 17/100 remaining
or for a free beta
Download now - 154/500 remaining
Obviously rewards are useful in other instances, but I think clarity around what you are purchasing is paramount - and at the moment it seems a little confusing if you have to buy a 'reward' to be able to download the game.
This would make it a very attractive platform from which to do closed beta tests. Just my 2 cents of course, feel free to ignore me :)