I've been using it for several years. I get my knives very sharp using this system.
This system works by your clamping a bracket onto the knife blade then using that to hold the stone at a precise angle to the blade. The problem is it's tedious at times because if you're sharpening a longer knife, you have to keep moving the clamp up the blade so you can sharpen the entire length. In other words, start with the coarse stone and sharpen a 3"-4" length of blade on both sides, move the clamp and repeat with the coarse stone. Then switch to the medium stone and repeat the entire process. The the fine and extra fine stones...
If I could justify the expense of the Apex system, I'd go for that, but this works for me and I have lots of time to do the work.
I have not tried the diamond stones.
"If you want to make an apple pie from scratch, you must first create the universe." -Carl Sagan