Fine or coarse knife sharpener?

Ideally, you want to buy both stones. The coarse stone is used to repair damage and put a rough edge on the blade (this is for really dull or damaged knives). The fine stone is used to polish the edge and get a razor sharp knife. If you are looking for a good sharpener that does it all, I can safely recommend the Spyderco Sharpmaker. It has both rough and fine sharpening stones and costs the same as one of the Buck stones you linked. Plus, it's a system that is much easier to use than a regular bench top stone. If your friend doesn't know how the sharpen, the Buck stones might actually make his knife worse.