While it may still feel like there is a lot to choose from, you don’t need a lot of of stones, you just a several good varieties to choose from. To summarize I will indicate below what my favourite stones are in each grit. Yes you can mix up the brands when sharpening but my recommendation is to buy a combination of 2-3 stones of the same brand and go from there.

Don't know. Not sure that I really care, as these stones definitely did the job that was asked of them, and did it with ease, even for a beginner whetstone user. I'll probably stick with them, at least until I get a lot more experience. Though, I do see a 10,000 or higher grit stone in my immediate future - more to play around with, than a feeling of genuine need.
I've used ceramic rods, diamond plates, and leather strops for our sharpening needs. And, like most, I've tried a dozen little gimmicky sharpeners that, while some work, those that do often remove way too much material from the edge, making your blade wear down faster. I've also used oil stones, grinders and buffers for less meticulous sharpening of axes and such. These two stones from Unimi (600/1000 and 2000/6000) served as my introduction to whetstone sharpening. And I must say I like it. Though, I'm not sure of the need for investing in more expensive stones.

Whetstone sharpener or sharpening stone has been here and there for a long time even before we born in the form of natural stone whatever they look like. Until today, the natural stone likely to be the most preferred options to sharpening things because of their versatility. As the technology improves, there are immerging new models and we are now not only having an option to the natural stone, but there are also other types considered better and more practical to use. The arrays can be bewildering to the inexperienced sharpeners that so often times many of them end up with a crap or wrong decision on stone type for their utensils.

I bought this and Unimi's 600/1000 whetstone at the same time. Curiously, reviews are currently blocked for their 600/1000 model, as amazon wouldn't let me leave one for it. Considering the conspicuous absence of reviews in the other stone's listing, one can only assume they're being censored for everyone. So, maybe I should be more critical of these stones, and use them a while longer before giving them any praise? But I've had a very positive experience with them so far, and the 600/1000 stone was the one I found most useful.

Japanese water stones – both natural and synthetic – are known for their superior sharpening performance, not only for Japanese tools, but also on their Western equivalents. The loosely bonded abrasive grit is washed out very quickly, as it blunts during the sharpening process; this exposes new, sharp, particles that can get to work on the blade. Water stones are lubricated only with water! Never use oil!

I've always wanted to sharpen knives on water stones, and this set gave me the motivation to finally give it a shot. The price is amazing for the quality and content of the set. It comes with all the grits you need to sharpen anything... I usually start on the 400 grit if the knife is very dull, or directly on the 1000 grit if it's not too dull. The 3000 and 8000 grit stones are softer and ideal after the coarser stones. The online learning section is truly amazing, much better than I expected. A convenient place with instructional videos and many articles about knife sharpening. Only downside is that the knives are now so sharp I need to be very careful using them... but that's a good thing! I feel like I fell in love with knife sharpening again. 

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.
I'm a novice knife sharpener. I've had to unlearn what my grandpa taught me in order to use these. So far, I've had decent but mixed results. I've switched to my cheap 200/400-ish cheap tool stone from harbor freight for cutting a bevel when the blade has either been damaged or did not have a proper bevel. The 400/1000 grit stone in this kit is soft. Very soft. I have bowled it out several times. It makes keeping a steady angle difficult. But these stones at this price point are meant for learning, and for that they serve their purpose.
Very interesting. If you work flat, 45 degree is what I was taught. Love the wet stones, especially the oiled ones. The nice thing about the leather part, is the mirror finish on a razor sharp blade which is a must if doing fine wood working, carving etc. A rough blade simply does not have the fine detailed dexterity. I find that the oiled sandpaper can work great as well, but found that the refined clay bars (white refined fired clay rounds and flats etc) does a wonderful job of keeping those razor edges refined, smooth as possible and then one can high polish them for smooth cutting. Believe me, when working wood for a flute, one wants that refined edge.! Learning how to hone a blade on a flat surface teaches one to work outside without a table/wall handy too...:) But we all have to start somewhere!:) Anyway, great stuff and a great start for those who want more from their tools!:) Cheers!
Historically, there are three broad grades of Japanese sharpening stones: the ara-to, or "rough stone", the naka-to or "middle/medium stone" and the shiage-to or "finishing stone". There is a fourth type of stone, the nagura, which is not used directly. Rather, it is used to form a cutting slurry on the shiage-to, which is often too hard to create the necessary slurry. Converting these names to absolute grit size is difficult as the classes are broad and natural stones have no inherent "grit number". As an indication, ara-to is probably (using a non-Japanese system of grading grit size) 500–1000 grit. The naka-to is probably 3000–5000 grit and the shiage-to is likely 7000–10000 grit. Current synthetic grit values range from extremely coarse, such as 120 grit, through extremely fine, such as 30,000 grit (less than half a micrometer abrasive particle size).[citation needed]
For a quick jump, you can see on the chart below made by Steve Bottorff described on his popular book Sharpening Made Easy: A Primer on Sharpening Knives and Other Edged Tools. The book tells many things about knife sharpening, sharpening system and DIY guide how to sharpen razor-sharp edges. If you want to surf deeper into the world of the sharpener, then it is one of a must-read book for you. For you who dwell in the Mainland or around the United Kingdom, you can buy the book through the link below.

The Sunrise Pro doesn’t have the pedigree of some other knife sharpeners on our list but it performs as advertised and that’s all that matters. For a relative song you get to restore all the knives, steak knives, cleavers in your kitchen to near pristine condition. It’s easy to use and the nice strong suction cup on the bottom means you can put the band aids away.

Some of the videos I watched suggested soaking the stone for 12-15 minutes prior to use. One suggested using vegetable oil on the surface versus water/soaking (I used water and presoaking it for 15-minutes). So instead of a simple 'out-of-the-box-and-use' approach, it required a bit of research before sharpening a knife. Otherwise I would have given this product a 5-star rating.