I am skeptical of the claims made for it - but have no first hand observations of its effects upon waters i have fished. I stopped fishing some local lakes just before it was used there and never been back - they were getting "gardened" too much for my liking (tree removal, installation of platforms etc) and were way too busy for my liking anyway.
To my mind the best and only way to reduce silt depth is to suction pump it out or to dredge it. Unless you were using siltex in some upland or acidic waterbody there is likely to be no beneficial effect on snails etc - virtually all waterbodies in the midlands or south are fine for snails and have ideal pH without liming.
As for invertebrates, it is the edges of lakes and ponds that are important - especially if theres lots of emergent plants - for wide range of invertebrates, water fleas etc etc. Bare silt is only good for bloodworms, mussels and a few other animals - a limited diversity - though large numbers will make good food source.
If the need is to get oxygen into the silt (to promote aerobic decomposition of silt by bacteria etc) then a good raking could work better. Also, dont forget natural aeration caused by fish stirring up the sediment as they feed, and from burrowing invertebrates that live in the silt.
A common problem is small ponds so heavily overstocked with large fish (eg carp) or birds (eg waterfowl) that a huge volume of excrement causes deoxgenation at the lake bed. In such conditions i would reduce the source of the excrement, increase the flushing rate (throughput of clean water), or introduce aeration.
Although i havent fished them, I have seen the after effects of using Siltex (or crushed limestone) on several lakes when coupled with use of herbicide targeting blanket weed. It has turned clear-watered lakes full of weedbeds including lillies into a barren pea soup as phytoplankton flourished.