Where should I buy Lubix, and is it worth it?
You can purchase it on their website, lubixcube.com, or some of the mainstream US stores such as SpeedCubeShop and Cube Depot. I believe you can also get it on Cubesmith.
I personally think it's really expensive for just a tiny thing of lube, and even if it can lube 15 cubes or however much they advertise, you can get Maru lube or just plain silicone spray for cheaper and it lasts for much, much longer (my only vial of Maru lube, for instance, is halfway used and I've lubed many, many cubes with it; and with my silicone spray, it's the same story). I think that Lubix works well on certain cubes (Dayan GuHong is a good example), but for other cubes you might just as well lube it with something else that's cheaper (Maru or CRC) so in the end I would say it's not really worth it. I don't have the biggest cube collection (only 6 or so 3x3x3s) but I've used Lubix on a GuHong, a LingYun, an Alpha V, Alpha V-f, and an F-II but the only cube out of that set that I would feel like I couldn't make that good without Lubix was the GuHong. The other cubes I've lubed with Lubix are nice, but not amazing at all, and I feel that I could have achieved the same goodness with other lubricant (Maru or CRC). And I've got 2 GuHongs (one lubed with Lubix (the Ultimate GuHong (I got it for free, otherwise I probably wouldn't have bought it)) and the other without), and I still like the one without Lubix a lot.
Overall, if you want to try it out or if you have a billion GuHongs lying about, you should get it. Otherwise, just don't because it's too expensive when you can get cheaper, just as good alternatives.
Oh, and I don't mean to be hating on the Lubix company, what they're doing is great; I'm just saying that the prices are a bit too high for the quality of lubricant that you get.