So there are some great points to using Stewart Systems and some not so great points. The real deal-maker is lack of toxic fumes. After all these years of torturing my lungs with nasty chemicals, it's worth the down sides.
The down side is that once you paint on the initial coat of EcoBOND (same green stuff used as the adhesive to glue the fabric on) to fill the weave, the surfaces can no longer be sanded in anyway. EcoBOND is basically a water-based rubber contact cement that once cured is completely waterproof. That is why Stewart systems recommends it. The subsequent coats of EcoFILL will complete the filling process and give you a surface ready to paint, HOWEVER EcoFILL is NOT waterproof. So unless you apply the base coat of EcoBOND your paint job will not be waterproof from the INSIDE.
I was introduced to this paint process by a friend and he did not know about this characteristic and used EcoFILL as the initial weave fill and has had great success with his paint jobs. Of course once you paint the Ecofill with latex or epoxy the outer surface is waterproof and in almost all cases this will be just fine for our RC purposes. However, for this giant beast I'm building I wanted it to be a sealed paint job inside and out so hence the green initial coating.
Now back to the down side of not being able to sand the green stuff. There are times when you would definitely want to sand that initial coating. At the seams there are always loose cut end and stray fibers that you could normally sand off if the fabric is initially coated with a sandable coating like the EcoFILL is. However, all is not lost: I discovered that once it's completely cured you can go back over all the seams and iron all the ragged edges smoothly down. The EcoBOND will melt/smear down to the surface and re-cure to a (mostly) smooth surface. The subsequent coating of the EcoFILL filler will be completely sandable and help to further smooth the seams. However, my friend that has been using this process says that the EcoFILL will not hide very much so we will see how all my seems turn out. Fingers crossed!!
Green = waterproof. And also unsandable!
By the way: EcoBOND comes in two colors: one is cream colored for see-thru paint jobs. I happen to have some of that to start and that is why my fuselage and other surfaces did not show the green adhesive under the cloth.