Welp, I just set up my 20 gallon vivarium tank. I used eco-complete for a substrate (one and a half bags were plenty for this smaller, semi-aquatic tank).
Anyway, here are my thoughts (so far):
1) Excellent color--a nice, dark coloration that isn't so black that it looks fake. Eco-complete is a nice, subtle blend of different colored gravel--hardly noticable, but enough to make the substrate look natural.
2) Absolutely no rinsing or cloudy water--and I have a decent current flowing through this stream tank! This is what originally sold me on eco-complete...I have had bad experiences with laterite and flourite in the past.
3) Plants (including glosso) were a breeze to plant and keep in place--not a single plant has come loose, and the gravel isn't all that thick (about 2-3 inches).
4) Cheaper than flourite--and 20 Lbs goes further! Go look at a bag of flourite and a bag of eco-complete...the eco-complete is clearly larger and (at least at my LFS) cheaper.
Of course, since I just set up this tank I have no feedback on the long-term benefits of eco-complete. So far, things are going well...