What is the difference between simply thinning down a brown color to simulate mud for example or thinning down black paint for grime and use of these products?Is there a really noticeable effect from these products?What products do you recommend?

Personally, apart of convenience I don't see other advantages of the ready-made products. You don't need to think about paint proportions when mixing a certain tone and they are always ready when you need them.

I have both ready-made mixes and oil paints. I'm using one or the other depending on the mood I'm in

I have a few ready made products, but see no advantage in them. I reduce ModelMaster/Testors paint for washes and it works just as well.

With acrylic based washes (going with my Vallejo experience), there is a difference. The washes aren't simply watered down paint, they have slightly different properties and can be used as filters and washes, plus they can be fairly easily cleaned up with a moistened cotton bud. I'm presuming the same thing is true of "weathering effects". The advantage these products should have (apart from convenience) is that they don't act like acrylic paint, meaning you have a little more working time and they can be blended in somewhat. You can make your own mixes of course, there are plenty of mediums available to make all sorts of concoctions for all sorts of applications.

Kimmo

Thanks for the responses,building my first kit in 30 years.I do not recall these products existing back then.

It's a whole new world of modeling these days.Pick up some books or magazines,or just search the net for articles and videos for an endless variety of products,techniques,aftermarket,and accessories.You can go old school or try out some new product.Only your preferences and wallet will determine what you do.

I second that on the Vallejo Wash products. Come to think of it I use it more as a filter.

I prefer the ammo products

In my opinion the main advantage is that they are ready to use. The exact shade and dilution.
You may recreate it yourself but will need some time to get the paint mix and some practice to get the right consistency. Therefore, it's very useful for beginners, or if you have limited time.

I tried to make my own watering down some Tamiya black.Did not go well,so I purchased Vallejo's desert dust,dark brown,oiled earth and Lavedo black wash(I think they made a mistake because I am sure I ordered Vallejo black wash).Works well on rivets and small parts.Can I use this as an entire filter/wash over the model?Can it be applied by airbrush?Not sure if I want to proceed as I do not want to ruin the model.I have applied a laquer coat to protect the current paint job.

the difference between wash and filters is just filter is more thinned then a wash,i speak about the ready made

Yes you can use it either as wash or filter. I just thin lt with heavily with water if used as a filter. I do put on a clear coat prior to applying. Airbrushed? Haven't done that. Aren't washes and filters supposed to be done by brush?

I would like to recommend you Ammo and AKI products. They could decrease your trial and error.

I always use the brush,for the wash the AB i dont think can works maybe for filters..

For decades, way before all these new washes and filters were available, the only way to weather was mixing your own weathering pigments yourself. And not all oil paints were the same. Pactra oils wouldn't mix with regular testors or testors modelmaster paints, regular testors would mix with moldermasters and humbrol wouldn't mix with anything and artist oils were best used by themselves. Each brand reacted differently with different brands of thinners and you had to experiment with paint and thinners to find out what paint worked with what thinner. I had about a dozen different thinners for all the different paints. Acrylics, when they came out, were touted as being able to be thinned with water, but that didn't work very well as washes. I finally found that for weathering early tamiya acrylics worked best with a bit a IPA for thinning. But the main thing I learned was after laying down the basecoat was to seal it with "dullcoat" or "glosscoat" depending if I was putting down decals at that point because the thin washes and different thinner would react with the basecoat if it wasn't sealed. And of course laying down a nice even layer of dullcoat once completed. I'm going to try some of these newer pigments as I transfer from strictly oil base to mainly acrylics, as funds are available. But I'm sure I'll still use my old tried and true, familiar washes for the majority of my weathering.

"regular testors would mix with moldermasters" I meant to say regular testors often would not mix with modelmasters.

Here is a feature explaining how to make your own washes and filters with a variety of model paints, artist products, and common fluids.

https://archive.kitmaker.net/features/782

I've found Lifecolor tensocrom to be really good. They make a range of premixed colours, for stains and washes, plus they sell the tensocrom base to mix with any colour in their range. Pretty much them make up any colour of wash or filter you need