Purchasable in quotes is because when you try to play, you get a required space to put a registration number– a number that’s not provided to you when you buy the game. I’m sure this will get fixed eventually, but I would wait until release to pick it up if you’re planning on it.
NOTE; steam users– you have to dig down into your steam folder to install the beta files. It should currently reside in VALVE/STEAM/STEAMAPPS/Gratuitous Space Battles/ Remember to CUT the last part of the path string the default setting gives you as it will try to create a new /Gratuitous Space Battles/ folder within your current Gratuitous Space Battles/ folder if you don’t.