Yes! I have used it to set up a 5G tank and it did work very well. Ammonia never went up to detectable levels and nitrites were just detectable briefly, and then went back to 0.
I read somewhere that there are some water conditioners that can interfere with it though so be careful what you put in your tank with it. Of course Marineland suggests that you only use it with their products.
If I remember correctly, it was like $12.00 US for enough to treat 30G. Kind of pricey, but worth it for no cycle time if you ask me.
Can't help you with where to order it. I got it at my lfs.