I bought the first episode through some indie bundle (Desura key) together with prequel comics. Then season pass from this website.
I admit I had been peeping at Cognition curiously since I heard about it for first time months after its Kickstarter success. Demo intrigued me but I was hesitant to buy it because Gamefly and others used region DRM for everything I was interested in (= don't browse these websites) and Rain store was very vague how they distribute what I buy. I dislike intrusive DRM (3rd party client, online check, etc.) and a lot of shops recently like to use DRM-free as a marketing lime-twig instead of serious use. That's why I like GOG. They are very clear at what they offer and how they distribute it.
My personal humble tip is to expand on the description. Say that the user gets non-expiring X download attempts directly from unique HTTP address and nothing else is required. No calling home and so on.
We do intend to get the game into GOG as well, once all four episodes are released, though! 
Awesome! I would like to see it there sooner now when GOG supports episodic content. On the other hand, a part of community is still suspicious of this release plan, so it won't probably hurt if you don't go down in GOG history as a episodic harbinger

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I'd probably buy a second copy there at some higher discount. Oh, and let's not forget the obligatory link to
Cognition page on GOG wishlist.
Now if you excuse me, I have important things to do; namely launching Cognition episode 2

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