It does what it says

Very convenient for cleaning the machine, and it also helps a little with the uniformity of coffee extraction.

The philosophy behind it is to have the water flow evenly for a better result and not just to avoid dirtying the machine internally. I use it and I noticed a difference regarding the cleaning of the machine after each coffee. Due to the higher pressure, it creates slightly more crema. In terms of taste, I noticed a slight difference, but the coffee seems lighter to me, which has to do with the tamping. With a factory basket with a small hole, a light tamp is needed. I uploaded a video for you to see various

I just put it on (De'Longhi Dedica) and the machine stopped splattering, so it indeed stops the water grooves. Theoretically, it also increases the pressure, since it adds another level that the water has to pass through, but I didn't notice a difference in taste. However, just for the convenience in cleaning the machine and countertop, it is one of the best accessories, especially for the price (I got it for 8.00 €)

Good for not staining the top part of the coffee maker and for the coffee to come out more properly in the bottomless portafilter.

It leaves some gaps around the slightly larger than 51mm baskets, but it does its job satisfactorily.