Since Substance Painter allows users to paint in full 3D, it can be used not only to paint full textures, but can also paint masks which can then be used in other tools (like Substance Designer) for material filter generators (like the ones used to make edge wear and dirt)
The free trial is the only thing free. You'll have to pay a lot of money for the full version, and even if you do get it, you will have to pay for an expensive graphics card to use it, which means a lot more money flying out of your wallet and/or bank account.
All maps will be resolution independent because of procedural techniques which MapZone uses. So you can work at a decent resolution, resize when done and you have a higher resolution texture immediately.
Filter Forge includes a lot of filters and each of them has several presets. Filters are grouped into different categories (Organic, Patterns, Creative, Distortions, Photo, etc...) so it's easy to locate them.