To chime in & add my two cents...
Its the wood that's adding that color to the water. Tannins. I have several pieces & of mopani & they all color up the water a yellowy-brown color within a weeks time. From I've read all over & IME, fish don't mind it whatsoever. You'll probably get a few people with that similar response.
I think the amount of tannins released is going to depend on the type of 'aquarium safe' wood. My 55g has 4 good sized pieces of driftwood & initially stained the water, but now it's all clear. Mopani definitely colors up my water, but I use it as a reminder to do a water change. After about 5 days, change 50% & it's crystal clear.
Anyways, I think that leaf zone rocks from what I've used it for. I've only used it with crypts & java ferns it a 10g. I definitely noticed a difference in the coloration & broadness of the leaves after a couple months of using it. It seemed liked the roots grew a lot thicker a few months after too. Who knows, maybe that's just the plant growing & adding the leaf zone was just purely coincidental. But I'm leaning towards no on that one.
Until I can get some flourish to go with my excel, I'm sticking with Leaf zone.
BobRoss