By itself the media takes a very long time to produce the desired result, however, with the addition of any of the liquid polishing compounds the results are rapid and predictable.
I have read comments that complain that the media turns dark or black quickly. This is normal and a sign that the media is doing it's job, just as a polishing cloth turns black when polishing brass.
This is not a sign that the media is spent. In fact, the media seems to perform better after it aquires a darker color.
I have cleaned several thousand cases in both rifle and handgun calibers without changing or adding to the media, with the exception od adding a capfull of polish now and then, and my results now are better and faster than when the media was new.
I do not know how long a batch of media will last, but it shows no sign of weakening. I suppose that at some point the cleaning cycle times will start to increase or the final results decrease, and I will have to discard the media, but so far it has held up very well.
The walnut shell media cleaned my 1927 FA brass very well. The batch had brass from 1927 through 1942, 30-06 military brass. What can I say... it works good.