Yes. Jonathan's prose clarity is an issue and his business would benefit from hiring a writer to go over it and interview him on parts they didn't understand and rewrite it for clarity. But the moly-fusion product I've had from him did what he said it would, and even though I haven't tried the phosphating materials yet, I did use the water displacing rinse he sells after using some older Brownells Parkerizing, and it worked fine.
Bill and Dixie are correct that the coloring agents (actually, growing selenium, nickel and copper microcrystaline needles that tend to trap light; it's like an electroless version of blue selenium or black nickel, copper, chromium, or platinum electroplating). However, I'll disagree that the solutions are overall the same in that the different surface activating acids used behave differently. Particular, the phosphoric acid types, Van's and Oxpho-blue, create thin phosphate conversion coating layers that are more corrosion resistant than the others, but which lack deep color (they are more charcoal gray to my eye).
The nitric acid based ones (e.g., 44/40) color deepest, and the hydrochloric acid-based one Outers had years ago (maybe they still do; I haven't looked) was most prone to after-rust. The latter two types etch the substrate to nucleate growth of the crystalline needles, but don't add the phosphate conversion that ties up free iron better to help prevent after-rust. Unfortunately, the phosphate also appears to lighten the color. Ferric chloride resulting from hydrochloric acid reacting with iron in steel promotes corrosion and deep rust knots that leave severe pits if you fail to get every trace of it out, so I can't recommend it. I always neutralize all cold blue work with an alkaline cleaner like Formula 409 afterward, then rinse and boil in distilled water to get that out, then soak it in water displacing oil. The only exception is cold blacking for aluminum, as the 409 will etch aluminum. Dishwashing liquid in water is what I use for that.
There are also mixed acid base versions. There was both nitric and phosphoric acid in one that used to be made in Canada twenty-five years ago. It was the best one I found for blackening sights. Very black (probably high nickel) and it boasted that it hardened over time, which it seemed to. It was much more difficult to rub off after sitting about 24 hours. Too bad it's no longer made.
I've used the nitric acid products on brass and copper before, but found the acid too aggressive and I got black flakes coming off the surface. So I've always assumed the solutions labeled for these metals had a higher pH to mitigate the aggressiveness. But I admit I've never measured their pH to confirm that guess.
Application tips:
Fine abrasive blasting as surface prep helps darken color and improve adhesion, too, but on steel it gives you a matte finish, so you can't use it where a smooth or polished finish is desired. I blast with 240 grit aluminum oxide from a Badger air eraser to prep iron sites for cold coloring because I want a really flat black there.
I've also had that problem with splotchy surfaces when using an aluminum blacking solution. I found that if I diluted it with 3 parts water, submerged the part (small heat sinks, in my case) and scrubbed the surface constantly with an old toothbrush during coloring, that got me 100% even coverage. I never tried it with steel blue on brass and copper to cure that flaking problem, but the combination of dilution and keeping any loose black carded (what the brush does) may fix that, too.