I use it in my pots (haven't got a planted tank yet, just pots, or jars, on a bare bottom).
As you can see, it's a very fine clay powdery 'soil'. Which means great clouds of muddy brown water if you disturb it, which is why I'm not planning on using it when I set up my tank. Okay for my pots because I make the mess in a bucket/sink, not the tank!
But it holds fine roots really well as you can see in the pic. Which means you'll also pull a lot of it up if you decide to uproot a plant!
It goes as a bottom layer below the gravel. The instructions say 2cm of Aquabasis Plus, then 4-5cm of normal gravel on top.
It's nutrient rich out of the pack, but depletes totally within four weeks, I guess to last through the initial set-up, after which you're supposed to add fertiliser tabs or sticks into the gravel to help (I actually add AZOO slow release fertiliser granules to it when I pot to last 3 months). Which means it's probably uneccessary having it there in the first place. Ditto if you're planning to use the EI method.
But it's supposed to be able to absorb and hold new nutrients from the water flow, so I suppose it's designed to need to work with those 'debatable' undergravel JBL heating cables to circulate water through it.
Hope that helps!