I use Rustall, although I think the whole 3 part biz is a little overblown. I say this because I primarily use only the actual rust wash. The other three parts are: A black wash, with a slightly blueish/purpleish hue; a flat coat; and a bottle of dirt (yep, dirt). The washes appear to be alcohol or water based, definitely nothing stronger. I rarely use the black wash (which appears to be an ink wash), because I find it tends to dry like most acrylic washes--rather blotchy. I've not used the flat coat at all, so I can't comment on that. And the dirt is, well, just dirt. It still needs to be sifted for most uses.
Now, those negatives aside, I will say that I love the centerpiece of the "system," the rust wash. I use this as my primary rusting treatment and it works very well. I just basecoat the piece in either black or dark gray, then apply several coats of the rust wash. A little bit of graphite or maybe silver drybrushing, and there you have it, an easy way to replicate rusty tools, tow cables, etc. The number of coats applied determine how rusty the piece will look. I'm not sure, but there may be a way to just purchase the rust wash. If that is the case, you will probably not be missing much by skipping the other parts of the so-called system.