You should be able to cap any substrate with sand if you wish, it's just that most manufacturers won't advertise the fact because your gonna buy less of their substrate.
If you like the look of it, go for it.
Just a bit of a bugger to stop the sand mixing with the substrate over time, and a bit of a pain to keep clean.
Hi, I havent used Tetra substrate, but I have seen good reviews, however JBL Aquabasis is a subsrate that worked well under silica sand. It is soil like and so smaller particles than the sand and therefore does not rise up over time into the upper substrate.
I use tetraplant complete substrate in my second small tank and I have to say is not what I want in other set up I use Polish made substrate which is "similar" to ADA product and works well obviously I have small problems but plants grown very well
in small tank I use same ferts (EI) and do not have same results
due to this I want to swap substrate in small tank for ADA amazonia and check how this work will see I will update later