The wavy design is probably just as strong as the double layer (possibly stronger depending on the direction of force). The issue with a single layer wall isn'

The wavy design is probably just as strong as the double layer (possibly stronger depending on the direction of force). The issue with a single layer wall isn't really the strength between bricks, or the bricks themselves - it's that a single layer wall has a very narrow base and is subject to tipping over. The wave in the design makes the base of the wall act is if it were MUCH wider, preventing the tipping action of a single layer. So the wavy design is only as strong as single layer of bricks, but it has a base 2 to 3 times the width of even the double layer wall designs. It will be much more resistant to tipping forces, but less resistant to impact forces. The thing about most walls is they aren't really load bearing - they just delineate owned space - so the wavy design is great for large properties. Much less great if it's a tiny space and you're losing a good chunk of sqft to the wave.