I used the eco complete a lot and enjoyed it, but then started to take a liking to flourite black and flourite black sand. I like to use them together as well, they look great together.
I've noticed more with the sand, but with both, that it has a noticeable amount of magnetic grains... I get them caught in my mag cleaners all the time. It's not much of a hassle but I see it as a pro and con. Yeah, it gets stuck in the magnet, might scratch the glass, but on the other hand it is adding iron. The plants seem to like it.
I'm a little worried though, I just started a tank up that's not planted, and used the flourite black sand because I had it around... hoping it doesn't mess with the tank.