Isn't it at least a bit suspicious that this guy is willing to sell you a popular and expensive item at
half of the
going price on Amazon, given that he claims not to know what condition it's in? It could be that the item is perfectly fine and he doesn't know that and just wants to get the thing off his hands. It could be that it's defective or broken in some way but he doesn't know that. It could be that there's something about the item that he's not telling you. You just don't know.
As mentioned, I've never gotten anything off of Craigslist, but my guess is that it's difficult at best to return an item, even a defective one. Besides, with something as complex as an X52, it might not be immediately obvious that there's something wrong with it.
Once again, it comes down to whether you like to gamble. Do you want to take your chances and spend outside of your stated price range on a used X52 that could be in any condition imaginable, or do you want to spend within your stated price range on a new Logitech stick that many people around here enjoy using? It's your call.