Well I don't know. The fabric must work in some applications or they would not recommend its use. I have never used it. I did notice that none of the walls pictured on their website were not vertical, they all lean into the grade.
The problem here is that a block wall depends very much on simple mass to work. The earth backfill is almost always going to have more mass than the wall, and as it moves it will push out against the wall. Time and pressure are on the side of the moving earth working against the wall. Proper drainage helps but as the earth settles it will always apply force against the wall.
Somehow you have to provide sufficient structural strength or enough mass in the wall to exceed this pressure. While I have seen a number of block walls that exceed 5 feet in height, there is always a lot of effort put into stabilizing the earth behind the wall prior to construction. I have even seen cement added to the backfill to solidify it.
Take the worst case – a timber wall. The wood has nothing near the mass of the earth it contains, so how do they work. Well, about every 2 feet of height requires installation of a “dead man” running back into the slope at intervals along the length of the wall to tie the wall into the slope (hopefully into undisturbed earth). As the pressure against the wall builds over time the outward pressure is offset by the resistance of the dead man. In some cases you can even install a cross piece on the dead man to increase it’s holding power.
Adding this kind of structure is easier with a timber wall than a block wall. With a block wall, there are ways to add similar structure but you have to be more creative. For example, you could run rods back into the slope with plates on both ends. One end ties to the wall, the other into the slope.
The problem here is that it does no good to anchor the wall into the fill you are trying to hold in place. The anchor will simply move and the wall fails.
That is why the recommended procedure is to add buttress supports at intervals. These can run back into the slope or be place in front of the wall. I have also seen walls that were built containing a number of angles in them to provide this same kind of support. But you have to do something.
IMHO block walls are best used to hold sand and lighter soils in place at reasonable heights. Heavier soils, hydric soils and taller walls require a different approach.
Now the wall that was the source of the original question here could be built in steps. Go up 4 courses and then move back into the slope a few feet and go up again, until the desired height is reached. I have had great success with this approach and it make for a great series of planter boxes where deep rooted plants can be used to help hold the earth in place.
