I've used Eco Complete, Floramax and Flourite. I think I like Floramax the best, the black version is Eco Complete without the bacteria and costs a lot less. The Original version is very similar to original Flourite, looks like flower pot rubble, but has a light flake in it that looks better than Flourite IMO.
I quit using Eco Complete for Floramax when 3 bags of it arrived via UPS frozen solid revealing how much of it is water, then as it melted all the dead special bacteria gave off a huge sulfur smell which took forever to rinse out. Can't be too special if I got it frozen!
Flourite is really dusty, I've been filling a big wire colander with it and rinsing under a strong stream in a laundry tub, then pouring RO with some Prime through as a final rinse. It can be cleaned very well that way, the same thing is done with Floramax but it goes faster. Doesn't seem to cause the abrasion and even more dust that rinsing in a bucket does.
They all work well, I have 4 Floramax Tanks, One Flourite tank and 11 tanks with both mixed and some of the old gravel substrate still remaining. I think Flormax grows plants better just because it has a lot of small particles and it's rough so it holds stem plants better; but Flourite holds rooted plants better, the granules interlock more and are heavier. Tank appearance drove some of the choices, black fish kind of disappear over a black substrate.
Some of these were recently started, some have been running for a year or two. The new ones weren't really cycled, they were started with canisters with mature media and a small amount of substrate from mature tanks evenly mixed in. About a cup or two for a 40B. After a day or so to let the cloud dissipate, lots of plants were put in and a few days later a few fish. Toxins were never detected and subjectively Floramax tanks started plants better, though the initial algae flush was about the same as for Flourite. Daily moderate pwc's were done for a week or so, then spaced out. AquaFertz root tabs are used in all tanks. I still haven't come close to mastering liquids, seems one drop brings algae.
Next one to be renovated will be MTS. I doubt I'll ever use plain gravel again, maintenance in a substrate tank that has stabilized is very low.