I have been using fluval stratum for some time now and I'll give you my two cents..
It won't break down as quickly as you think. It will take some time, probably 2 years or more (I noticed after 1.5 years parts of the stratum were disintegrating but 90% of it was still intact). It is also relatively inert so you will have to add some substrate tablets to fertilize your plants. It is also not recommended to mix with sand or other substrates because they won't mix well since the stratum is relatively light. It will not float but its dust will settle quickly which is nice if you have to disturb the substrate. I wouldn't recommend this substrate for bottom sifting fish like corys. My shrimp certainly enjoy sifting through it!
Let me know if you have any other questions