Rust bluing was used for centuries before hot salts bluing ("tank bluing") was invented. Done right, it not only is as durable as tank bluing but is (IMHO) much better looking. It is also the only way to go if restoring a firearm that was originally blued using rust blue.
As you have found, there are the slow bluing and the faster type that uses boiling water to hasten the process. I have used both and they will give comparable results if carefully controlled.
I recommend you buy an old rifle or shotgun from some gun shop's junk box and practice (a lot) until you have the system down pat before starting on anything good. Distilled water is often recommended because minerals in tap water can affect the bluing, sometimes for good, mostly for bad.
Remember, though, that metal preparation is the key to good bluing, regardless of the type used. That does NOT mean, as some gunsmiths seem to think, polishing to a mirror finish. That will work if you want a mirror finish. With tank blue, it will look fine on a Weatherby, but no factory guns were that highly polished and on anything else it will look artificial.
With rust blue, you will not get that mirror-like shine. Take a look at an early Luger, if you can find one, and you will see rust blue as it should be done.
One big advantage of rust blue is that there are almost no dangers (aside from boiling water if used) and some slight odor. Hot tank bluing can be very dangerous and the caustic salts can cause serious injury. The fumes require extremely good ventilation, too, to prevent health problems.
You can get the bluing from Brownells and it comes with instructions. A humidity box is nothing but a box, usually made of plywood, with a water pan and a couple of high wattage light bulbs. It has to be as long as the barrelled action to be blued and usually about a 1-1 1/2 feet square. Hinge one long side as a door that can open, and make the box to stand on end to make it easier to work with. One I used (not mine) had the door made
of plexiglas so the progress of the job could be seen without opening the door; I liked that idea.
The work being blued is suspended from wires hooked to the wooden plugs in the barrel, not to the gun itself. Grease and plug the barrel to keep from bluing the inside. Not a big deal if you do, but some people go ballistic if they see bluing in a barrel.
Jim