Interesting site and the guy is a wildman to watch. I find it entertaining.
The Eco/dirt question has been covered in 2 pages already.
(imo) Eco has been mineral treated and shipped wet but is basically inert. Soils are completely different.
Mineralized soil is a process that's involves many steps and the end result is a nutrient rich readily available base. NPT or simply dumping the dirt in and capping it are the same processes at work only at different times as the same thing happens. It's just a question of where, and how much work you do. Mineralizing the dirt is the activity of bacteria breaking down the organic compounds releasing the minerals. Making MTS this happens on a tarp in open air. The activity of bacteria breaking down the organic compounds over time creates several changes within the tank that MTS completes first eliminating these shifts from occurring in the aquarium. The conversion of organics and the break down is also slowed greatly in the tank because of less available oxygen. The submerged steady state of decay once established in the tank takes about a year to happen. During that time settling or collapse of the organics reduces the thickness of the substrate. This doesn't happen using MTS. The organics have been consumed / converted back to mineral content alone by the bacteria before the dirt ever goes in the tank. Biggest difference between the two, MTS and NPT is where the organics are broken down, in tank or before.
Be it MTS or NPT based on ease of upkeep and growth results dirt works used in either form and is the cheapest way to play.
I see a dirt tank this way; Lowest cost for setting up, no 'required' attention to dosing ferts on a schedule.
There is a fair amount of ongoing debate on which to use MTS or NPT.
I've done one MTS system and eight NPT based tanks so my choice is obvious.
Duration of useful tank life is also always debated.
This is my oldest dirt tank. I used only 1" of MGOPM setting this one up.
I have included some clays a couple times now to increase Fe and used the additions listed for mixing when setting up MTS tanks in newer natural soil/dirt tanks.
Having this tank set up with Potting Mix (dirt) alone (MGOPM) and capped with Flourite. Nothing else was really needed for over a year. I saw nothing to indicate the plants were lacking any nutrient at all and growth never stumbled. After a year crypt growth slowed, leaves grew slightly smaller. Now beyond 2yrs. setup and still no additives or changes made to the substrate. Growth has slowed but the tank is still stable and growing plants. Adding the other materials (clay and other additives) years from now I'll let you know if it matters.
The organics (mulch) in MGOC is 'fluffy' when dry is the best I can describe it.
Pressing it down so I can judge what I have helps to get a consistent 1.5" layer setting up the tank. Months down the road as the organics break down this 1.5" layer will collapse to less than half that thickness so I hold back capping materials so I can add it later maintaining the cap and adding depth along the way as needed.
A new tank I'll get everything wet and wait guessing 10 days to be the average. If the soils are going to release ammonia into the water creating a spike that will harm fish I've always tested rising levels within the first week.
flooded 4/30/2009 this tank is still growing plants so what exactly is lacking?
The comments posted above regarding potting mixes containing peat moss, vermiculite and/or pearlite, Dolomite/limestone (for pH control), and probably a water absorbing material/gel of some type simply is the WRONG STUFF.
Just on the limestone alone:
Adding anything to a soil base or a filter that effects carbonate or mineral hardness is something I don't recommend doing. Once it's in place you have lost all control of to what level hardness will reach. Equilibrium with the material exposed to water circulation now controls and I didn't like that. Once it's in the substrate and the tank is set you can't remove it either. At least in the filter you could. I did a couple test tanks (10g) trying limestone and a couple other materials and just wasn't comfortable with the results. That's why for bagged materials I recommend only the branded product that I do.
Natural soils and organics I'm good with and you'll always have unknowns to some degree using dirt. (Not packaged for our use) But I would avoid things known to affect the water hardness unless you are certain you need it. Using anything with 'infused water soluble nutrients/fertilizers' is asking for trouble.
Hope this answers more of your questions OP.