Just from my personal perspetive.....I believe Nitre Blue is ideal for knifemakers... all you need is a steel vessel (I made a couple of different ones from different diameter pipe, that I lopped off to the depth I wanted, then MIG welded a "cap" on one end that was 2x as thick as the pipe wall thickness. I retrofitted an old coleman two burner stove to propane, and been using it ever since (about 10 years now). The other produt I really like, but its no longer avaialbe was "black magic" salts that Jantz used to sell.
There are a number of different methods that can be used to "blue", but overall I've found Nitre Blue to be the simplest to use, and one of the more durable blue type finishes.
Another method of coloring that I've used successfully for a few years now is Gun-Kote.....it takes a bit of experimenting to get good results, but it can be had in just about any color, and most recently I have been using the clear satin to coat 416 laminate blades (the etch finish on those type blade is very fragile).
About the only drawback I can think of on Nitre Blue is that shipping costs.....they slap a hazardous shipping charge on, which nearly equals the cost of the product. The up side is that I've been using the same "batch" for nearly 10 years....so the longevity kind of offsets that additional shipping.