I used both successfully. More important, in my experience, is the top layer.
The potential clouding issue with the Tropica may be a concern if you plan on re-scaping your layout regularly, especially if you're using big rooters like crypts. However, unless you're performing a massive overhaul, then regular uprooting of the odd plant followed by a decent water change will clear up the clouding no problem.
Power Sand Special is basically peat-covered pumice granules. The 'Special' bit is the extras i.e. Bacter 100, Tourmaline BC and Clear Super. The peat provides lots of nutrients and the hard pumice allows for greater oxygen penetration down there. The other products claim to add bacteria, extra trace elements, and toxin removal. I have to say that in combination with ADA Aqua Soil Amazonia I have never experienced such impressive plant growth rate and health. This is purely anecdotal evidence, of course.
Tropica Plant Substrate is a clay-based product with high CEC (cation exchange capacity) that basically is the ability to take in nutrients from the water column, making them available to the roots. It turns to a mud-like substance as soon as water is added, and as mentioned it will cloud the water if it's disturbed. It may be advisable to cap it well, but I have only covered my latest set-up with Tropica topped with just a flat 4cm of other substrates (EcoComplete, Unipac black and Flourite Black mixed).
Before we get into a big, "is ADA worth the extra cash?" then it's important to know what your top layer is.
If it's ADA Aqua Soil then I'd consider the Power Sand Special.
If it's another type, then I'd go for Tropica.
They both work well, but if you're going for the ADA system, then it can be a go idea to go the 'whole hog', IME. The results cannot be denied.
I hope that helps.