It is free for quite some time. I used it already some years ago. And I can really recommend it. I find it better than some expensive or less expensive texture generators. For me it was the best one.

But on the other hand you always see the procedural generation, it never looks absolutely realistic. I personally prefer to model the texture as real mesh and render it out in Modo. It takes the same time or is even faster compared to creating all these procedural nodes you would need to get the same result.

The advantage of something like that (substance) in a realtime game is: You have smaller files to download. But the customer does not really have an advantage. The textures will be created during the first start of the game and will be stored on the HDD. So in the end it takes the same amount of memory on hard dics and in memory as any other texture.