I haven't had any issues with FS and didn't require a large amount to achieve what i wanted to do with my nano build. I don't deny the effectiveness of ADA AS, by all means continue being a fan.. I just didn't feel like paying $42.99+ tax at the LFS for 18lbs of ADA AS Amazonia when i can achieve the same thing on my GLA 6g with a 4.4lbs bag of FS to top some cheap but effective Floramax for a mere $12.
In terms of ADA AS, I would say I'm a fan too. I can't deny how well some of these planted tanks look with it on TPT or here like Fort's 12L.
Now on FS, I created a substantial slope on my 6g GLA build and still have FS leftover. So simply buying ADA AS, even if per unit price is comparable, would be just waste for me. I believe since Dan has the same tank as mine, i only suggested an economical route to achieving the desired look. Although i haven't tried ADA AS, I'm quite pleased with FS because my HC has carpeted fine in it and all my stem plants have grown to my liking.
If i had a larger rimless tank (hint: coming in the not so distant future) that required a lot of substrate, i certainly wouldn't overlook ADA AS as an option if my budget permits it and is suitable for my needs (not just to buy and stock a surplus of it). Because we all know how much of a money-pit this hobby can be once you factor EVERYTHING in (e.g. lights, filter, fish, plants, ferts, etc.), I personally find it wise to cut costs where possible.
On a side note, nice compiled spreadsheet on substrate prices.. I think it would be useful to others and it deserves its own thread similar to the LED Lighting Compendium by samamorgan on TPT.
Edit: one other factor that should be brought to light in that data comparison is shipping cost. Even the smallest 3L bag of ADA AS is only $14.95 on ADGshop, but with shipping, to my location, it's about $28 total. Whereas, FS ships free with Amazon Prime... other factors involved here such as local availability vs. having to order online, so mileage may vary with all things considered. SORRY for the long post everyone.. it wasn't a simple answer to my justifications.