I recentley set up a small 6 gallon planted tank and i used Eco Complete substrate. It has been a very good substrate and my plants have been thriving since the day i put them in. Granted i am only doing a low maintenacne set up with ony 8 watts of lighting with low-medium light plants (crypts), they have been thriving and I have seperated new growhts about three times already.
I have researched this product and about 85% of the reviews on Eco Complete have been posittive. Some people noted that their was a little bit of leeching and compaction but more often than not it was recommended.
I am just throwing this possibility out there, so if you want to, feel free to research Eco Complete Substrate.
Lol, but i too feel very curious about kitty litter and may try it the next time i set up a planted tank.