You're going to get a lot of different answers and in reality, there's really no true highly recomended or correct product to use. With so many out there, no wonder you're confused trying to get the best of whatever product is there. I have a couple and I also use the cheap way of weathering as well using chalk. So simple, even a caveman can do it.
Here's what you do. scrap the chalk into a pallette dish using an edge of a hobby blade. (you want to get the dust like particles)
Add a little bit of water and a drop of dishsoap (yes... you read that right - dish soap. Stir up up good until blended.
Now get a brush and brush your kit all over it. Don't worry about brushing too much on the model. It's impossible.
Let it dry overnight. Seal it in with clearcoat.
Experiment it on a junk kit and try for yourself.