At the risk of getting flamed, are you considering the behavioural angle? A circuit with four legs at right angles neatly segments the workload and decision making into four phases with no overlap should you choose not to have any.
It also makes the traffic management (we do have six in the circuit on weekends, and since its parallel runways there are contra rotating circuits.) somewhat easier, especially with newer students.
I suggest that when the going gets slightly tough, like landing with a crosswind on an unfamiliar airstrip after a bumpy and long flight, the four phases of the circuit help to focus on the task at hand and hopefully not miss anything, especially for low time pilots like me.
I've made a few circular approaches ( gliding approaches) and while they are fun to do on a familiar field, I'm not so sure I'd like to try it in an unfamiliar location, like this one.
