This is not a bad deal: thirty-eight Discworld novels for eighteen bucks. I mean, yeah, I have them all already, and you can tell the precise moment in my life where I could afford to buy Terry Pratchett in hardcover. Still, it’s a damned good Humble Bundle offer.
One caveat, though: you’ll need a Kobo account. I have no idea how difficult it’d be to get those books out of there, and into your Kindle reader. …And I suppose that the fact that I have to make that caveat tells you quite a bit about Kobo that the platform would prefer you not to dwell upon.