The small bricks are layed differently here. In my country, the morter is mixed real soft. Here, using the small bricks, it is mixed stiff. I'm not sure why.
Having said that, I would think mixing your own would be better because you can adhust the firmness. But, if you've only got around 200 or so to lay, ready mixed would probably be better and you won't have a pile of sand left over in your yard that you don't know what to do with. IMHO.