I cannot speak for other peoples' experiences but I have a 3 gallon low light, low tech nano at work with a cap of Tahitian moon sand capped over a dusting of peat and leonardite. Java fern, anubias nana, and ambulia are thriving, but the dwarf sag is not doing too well and the cryptcorne melted and never recovered. The Amano Shrimp and White Cloud Minnow are still alive and kicking.
I have another 5 gallon low tech, low light tank tank with a cap of Seachem Onyx sand capped over a dusting of peat moss and leonardite. Amano Shrimp, Dwarf Frog, and otocat are alive and kicking and have been for several months. There is a smidgen of black bursh algae mostly on some ambulia and cardamine lyrata plants, but this may have more to do with frequent water changes than anything else. Otherwise, plant growth is much better in the 5 gallon. The cryptocorne never melted from day one and even sent out another runner, ambulia are growing slowly but thriving, hygorphilia polysperma is thriving, anubias nana, java fern, and apongenton plants are all thriving.
IME, plant growth with the Seachem Onyx Sand, at least for me seems better than with the Tahitian Moon sand, with all other things(except) tank size being equal.