These 2 brushes are not simple "stamp" brushes but rather have scripts associated with them which will give them variance when applied.
Each has also some degree of jitter effect to randomise position, size and other attributes.
I found them useful to provide background texture in a slightly random grungy fashion.
Commercial Use OK
Full terms of use with the brushes in my Free Download ZIP
Have fun ..and I'd love to see what you do with them :)
An example HERE