We finally got some clay brick but started with cement block just so they could go to work. Both bricks are nearly the same size. There is a regular brick and an over-sized. We're using the larger which will use less cement and go up faster - the problem is they are not as easily found and do cost more. The first section laid is a meter high so the weight does not compress the wall. One meter is also the standard window height
The bottom foto shows how when working with block, they insert a few rows of clay brick because clay is more flexible and will relieve earthquake stress on the walls.