The following are my personal favourites and they are all synthetic stones, I do have experience with natural what stones but lets keep it simple, lets stick to synthetic water stones. Believe me, some of the world sharpest knives are sharpened solely on synthetic stones. Here are my personal favourites, I use these water stones every day and the order is not necessarily in priority, they are all good. 

Put the pointed, narrow end of the sharpener up against the open end of the gut hook. The narrow, pointed end of the sharpener should face in toward the thickness of the blade, away from the edge of the gut hook. Match the angle of the sharpener to the original edge angle. This will maintain the correct sharpening angle and prevent you from getting cut by the blade tip. Hold the same angle when sharpening each side of the gut hook.

I recommend it as a lightweight alternative to larger stone for smaller knives. Leather necklace is comfortable and seems strong. I conditioned it for suppleness and swim with it on tightened as a choker. Stone is small, dog-tag size. I use it with water. Functional for small folder knives and multi-tools. Not useful for large fixed blades, since you can't make a long stroke. Small to grip. I use double-sided tape on one side to keep it in place on a flat rock. Not sure of grit, seems like around 1000. It took a while, but i got my old boy scout knife sharp.
My first set of sharpening stones so I have nothing to compare them to. For $50, though, great price to get into the world of sharpening. Stones are great and easy to use. Was able to put hair shaving edges on knives. Took a couple of knives to feel comfortable and better with the process and how to sharpen, but the stones you get work great. Here's the secret though. Get the green leather stoping block as well. As great as the stone are, I have found that stroping the knife after the fact is what really brings out that razor edge. And after using the knife, stroping it again, will restore and keep it razor sharp. Hope you enjoy it as much as I am.