I don't have any real experience with this product yet, but according to Jon Warner (of Warner Marine) they are slightly more effective at PO4 removal. Of course, he might be slightly biased
What most people seem to like better about the EcoBak pellets are the cost of course, and the fact that they require a lot less flow because they are made to not clump together like the NP pellets do. Also, at $20 less the price difference is a big plus.