I actually have not used them, but not for lack of trying. I have several very close friends that have used them.
In that case, don't go with the black beauty... but the others will be fine as long as you wash them well. They're all totally inert.
(The SMS and Turface can sometimes affect kh and, as a result, ph... If you soak it in tap water for a few hours, rinse, and then use it, it works like a charm.)
The SMS and Turface are 'fancy' versions of this product-
only smoothed out and colored.
Oil Dri is SUPER cheap- Roughly $3 for (equivilent of) 50 pounds. I have it in nearly all my tanks right now, but it's not black.
If you don't mind a variable medium gray, then try it. It's sold in the automotive section of wal-mart. I've heard it's safe for cories, but I've never tried it. Not sure if I'd risk it or not. I can't find any pictures of it, but for $3, go buy some and look at it for yourself. and post a picture for me.
If you want a planted tank, then instead of soaking the Oil-Dri (or Turface, or SMS..) in water, Mix up some fertiliser water in a pitcher- fertiliser brand doesn't matter to be honest- I use miracle grow now.
Make it strong- I use about 3 tbsp of miracle grow in 1 gallon of water.
Then pour that onto the DRY, BRAND NEW, turface/oil-dri/SMS. Let it sit for a little while (I usually let it sit for an hour or two.)
Then add enough water to the oil-dri to cover it, and let it sit as long as you want. (I let it sit for 24 hours)
Then rinse it extremely well, and use it in your tank.