I've used Amazonia, Fluval Shrimp Stratum, Eco-Complete, Flourite Black, and I have a walstatd bowl.
I just purchased Rio Escuro-XF. I added distilled water reconstituted to GH 1 KH 2. PH was 6.8 right before I added it. I haven't added the filter yet since i'm interested to see what the readings will be tomorrow.
So pending what is going on with the buffering capacity my initial opinion is. AWESOME!
It is totally black and looks awesome. It has a clean earthy smell. When I flooded the tank there was no cloudiness at all. They apparently already cleaned out all the micro-fine material that causes that to happen since there wasn't even dust in the bottom of the bag.
The granules are definitely firmer than amazonia. I pulled a small piece that has been soak for about 4 hours now out. I squeezed it to see what happens. With shrimp stratum I squeeze a pellet and it turns into fine dust, with amazonia it turned into mud. With the new substrate it just kind of compacted like a sponge which makes me think it will retain shape for a long time before going to mush.
I'm going to be using this mostly for moss but the particles are about as heavy as Amazonia 2 so it should be fantastic for planting (much better than shrimp stratum)
It is inert so if you plan on having root feeders you're better off with the amazonia.
so far LOVE IT!