The product is very good, and I think it's awesome that you're embracing bitcoin in connection with such a fine product.

Is this essentially just a donation model then, so the game will be free on the Apple Store and Google Play, but invite people to donate?  I can't see how you could do it as a normal pay-before-play or pay-to-unlock store, given how those services operate, but maybe that wasn't your intention anyway.

Note that asking people to tell you which address they donated into your account from is weak - anybody can look up the records of who has donated into the account, and claim to be responsible for one of the addresses.  If you care enough to only give the beta to people who have donated, then you need a stronger way to check you're giving it to the right people.

I also think there's enough of a barrier to entry into the bitcoin market that you'd only get these donations from people who are already using bitcoins - you need to be aware of that from the start.