I can't believe the complaints this is generating o_0. If I'm being honest, I think some of you need to take a step-back.
It's an *optional beta*. Emphasis on optional. As someone else pointed out, you can just wait until the final release if you feel paying for use of the beta is not justifiable. As someone else pointed out, this also seems like far more complete of a "beta" than most products that use that label release; you're essentially paying for a complete copy of an RPG core rulebook.
Will the product be different later? Hopefully yes, because that's the point of the beta. But does that mean that while playtesting this beta, you aren't getting the full experience of playing an RPG, since as been pointed out this is essentially a full release minus some artwork and fluff? Yes, you are. Whether that's worth $20 is *completely up to you*.
But to throw a fit because they're charging for a chance to play the game is absolutely ridiculous. Perhaps other companies do it differently, but they're different companies with different products. I would never play Pathfinder as a system, so how it does its betas is completely irrelevant. I love the 40k universe, I love how FFG has done its 40kRPGs, so I'm happy to get a chance to try out this new system, especially considering $20 for a full system is far cheaper than the usual $60 price tag core rulebooks come with.
Sure, if you give feedback you're "working for free." If that bothers you, buy the product, don't give feedback. But I view it as a chance to improve and enhance a product that I'll hopefully be using for years to come, and I'm happy to do that while doing something I'd do in my spare time anyway (play RPGs). So if I can play something I love to play while simultaneously helping out the company that makes it, I'm happy to.
And if you're not, just don't buy it. It's that simple. Complaining angrily on the forum isn't going to accomplish anything. Please take a second to step back and reconsider your perspective.