I find them particularly useful and use one in the rinse bucket and one in the wash bucket. Even before I had them I was never one to go anywhere near the bottom of either bucket with my wash mitt.
In my opinion, since using them I have found my black daily driver is benefitting. At the end of the wash there is a whole heap more dirt and grime under the grit guard in the bottom of the bucket than I used to find pre-grit guard, and the wash mitt itself is a whole lot cleaner. I don't think that can be a coincidence.