Intro

Vantage Modelling Solutions (VMS) is a company who has a good number of auxiliary products for modelling, from glues to airbrush cleaners and thinners.
Some of their products offer a great flexibility to use, allowing to fine tuning the effects.
Their website (https://www.vms-supplies.com/) is an excellent resource for using the products, with detailed text explanations and links to instructional videos.
From their range, I have tried four of their products, all of them related to pigments.

The products

ENML 2.0 Pigment Binder
This is a pigment fixer, whose most important feature is that it is reversible. That is, any time (from hours to weeks) you can remove it using Universal Weathering Carrier. It is affected also by Turpentine or White Spirit so if you plan to use these products on top, you should protect with varnish.
There are three types, for matt, satin and gloss finish. I have tried only the first.
Alkyd Pigment Binder
Another pigment fixer, but this one has limited working time. Within the first 24 hours you can remove it with Universal Weathering Carrier, however after this time it will be definitively cured.
Again, you can get it for matt, satin and gloss, of which I have used the matt one.
Universal Weathering Carrier
A simile to White Spirit, useful for thinning enamels, oils or their own products like the ones above mentioned.
Despite other brands of White Spirit have removed the fixers, this one seems to be more effective.
Pigment texture
A white dust that adds texture to the mix. Pigments alone need a lot to build up, so adding this product allows to save pigment and get some volume. It is useful for mud.
There are mid and coarse types, in this case I have used the latter.

Note that they offer also a wide range of pigments, available in different shades and texture. Although they may perform better, I have used the pigments I have at hand.

In use

I have tried the products on a scrap kit part and a wheel, both painted with Vallejo Model Air and without primer or varnish.
I divided the part in different zones so I could test the products side by side.
First I mixed the ENML binder with some third brand pigments. They dissolved easily and produced a thick, brown, liquid. It was easy to apply with a brush, but I think a matt base but have worked better.
Next section received the same liquid but adding the pigment texture. As expected, it became thicker.
Finally I used the Alkyd binder on the third section; it worked like the ENML 2.0.
I added also some splashes with all of them. For the wheel, being quite smaller, I used only ENML 2.0

I let it dry for approximately one hour, although using a hair dryer speeds up the process.
After that, a dry brush removed part of the pigment, and a wet one with Universal Weathering Carrier completely cleaned it. Both ENML and Alkyd were easily wiped, although I could not produce a soft edge. Maybe I should have soaked the area.
The next day I tried again to remove the pigments. As expected, the ones applied with ENML went away easily but the Alkyd one had became permanent and was no longer affected.

Finally, on the back of the part I tried to use the ENML binder in a more traditional way, dropping it over the pigments. While still wet, I blended one side with Universal Weathering Carrier to soften the edge.

The photos show how I have used it, for the purpose of a test and without intending to get realistic results at first.

On the wheels of the Sd.Kfz 251 I have used the Alkyd binder and three layers of different shades. The darker one has also satin varnish for wet appearance.

Conclusion

I found VMS system extremely useful and versatile, despite I still need to work more with them. Flat parts need more practice (for me), while for wheels it is really easy to get satisfactory results.
The ability to correct them for a long time is great, and specially for wheels and tracks it produces a nice dust and/or mud effect with little effort. The ENML binder is appropriated for a final application of pigments, while the Alkyd allows layering of different shades easily and safely without affecting the work below. In any case the paint was affected at all.
The Pigment Texture is an interesting add on as well, providing mud texture to pigments.

And this is only the tip of the iceberg: these products have also other uses, like filters or washes, and there are variants for satin or gloss finishes, and you can vary the ratio of pigment/fixer for different results...
I recommend a visit to their website and spend some time with the videos there, it is worth the time.