We received a litter box that is entirely gray instead of gray with yellow-green color in between, as shown in the photo. It is of good quality, fits most spaces, is a satisfactory medium size, and is elevated so that nothing comes out during the cat's digging (maybe 1-2 pellet grains).
I believe it works better with sand.
We use pellets, which do not sift through the specific holes. Nevertheless, the double litter box is useful, as I use another suitable sieve and the crumbs fall into the "backup" box, so I can dispose of them.

It's good as an idea. The problem is that with some clumping sands, like for example with Cature Tofu that I happen to use, it can solidify between the holes of the sieve, which makes cleaning very difficult afterwards.

The solution I found was to empty the sand inside the sieve instead of having it permanently under the sand, which however increases the number of movements I have to make. Furthermore, because the Cature Tofu I use tends to stick to the bottom of the litter box, I have to use the scoop anyway to detach it. So, it defeats the whole purpose as they say.

In general, I found that in the end it takes me more time to use the sieve compared to scooping the sand with a good and especially large scoop. So I stopped doing it and just use it as a regular litter box without the sieve.

Finally, in terms of size, the litter box is a bit smaller than I expected and as my cat grew up, she started to not find it so comfortable. So my final conclusion is this, don't get it if you use Cature Tofu or/and if your cat is not relatively small in size.

I consider it to be a very good toilet. It provides you with 2 bowls, so you can be comfortable as you use them alternately. Of course, it is not suitable for thick pellets (such as Cat's Best pellet) as they do not pass through the sieve. It was easy to clean with Cature pellets.
I use a scoop to clean it during the day because I can't constantly change and wash the bowls. As for dirtiness, I would say it depends on the cat. Mine makes a mess, sometimes she goes inside and throws pellets out to play, so I constantly clean around. I don't know about using sand... with pellets, as I mentioned before, it is convenient, but again, the scoop is necessary even to push the pellets that get stuck in the passages.

The grill as an idea is good, but in practice it is not convenient since the ashes that solidify with the sand stick between the cells of the grill and need to be scraped off.

The cleaning time has been reduced by 80%.
We have 5 litter boxes in our house, as well as 4 cats, so cleaning the litter was quite time-consuming. It used to take us about 20 minutes for all 5, but now we finish in 5 minutes. And I only bought 1, using it as a sieve for all the litter boxes. If we had 5 of these, it would be perfect, but they cost 30€ each... as if you're not buying a simple plastic litter box with a sieve.

Update 17/7/23:
Although the process is much faster compared to the scoop, after a few days of use, we started using the scoop again, because:
- it is relatively heavy to lift the litter box with all the sand inside
- when returning the clean sand to the litter box, it is very easy to spill it outside in a considerable amount
- a lot of dust is raised during this process

Maybe it's okay for one litter box, but with the 5 we have, the chances of making a mess afterwards increase significantly. Whereas with the scoop, it is much more controlled.

Although a bit expensive as a product, this specific product is not just a simple litter box but consists of 4 plastic pieces. 2 litter boxes, a sifter, and the protective plastic around it to prevent the litter from falling out. It is very convenient as it allows you to easily sift the litter from one box to the other, eliminating the need for scooping with a scoop. It saves a lot of time and definitely does the job correctly because it captures everything, while with a scoop, you tend to forget something. Ultimately, I believe it is worth the money, although it could ideally be a little cheaper, around $25 instead of the current $30-32.