Fair enough. I know that some third party abused of this beta system, but I dont think it will be done again. Look at Razbamfor example, they released the mirage very early and have been fast in fixing it and getting the remaining features implemented. Even if they asked for a full price it wasn't that bad.
I trust Polychop about this as well even if they release an early version, which I think they wont, or a beta, I wouldnt have a problem to pay full price as long as they are committed to finish it.
Third party devs are small studios and the market they target is really small. Paying full price is giving them support and even keep them alive. I am not disappointed by Razbam and I am confident I wont be with Polychop.