I've been using it for the last few months, and liking it so far! I started becuase i read about how the glycerin in "pastey" tooth paste coats the teeth, which prevents the saliva from coming in contact with the teeth and re-mineralizing them like it should. I noticed that some discolored spots on my front teeth dissapeared after using it for a few months, and the color of my teeth looks more even overall.
Probably the most "natural" thing to use would be to make your own tooth powder out of clay, baking soda and salt with a little mint e.o., which is what I originially used for a while until I decided to give Eco Dent a try. I am still on my 1st bottle, and its only half gone, so its very cost-effective! : ) It definitly tastes better than homemade toothpowder, and has something in it that makes it foam up when you brush with it, which is also nice but I'm not sure if that's necesarrily a good or bad thing...LOL. Proably makes it a bit more harsh on the gums than stuff that doesn't "foam".
I still haven't decided if I'm going to re-purchase it once I run out or if I'll make my own next time...
hope this helps!