The run and break was originally designed during hostilities to prevent aircraft being shot down by enemy aircraft. An aircraft on long straight finals in the landing configuration prevents an easy target to a following fighter!
The manoeuvre gives very little time for an enemy pilot to draw a bead as it gives a constantly changing flightpath and a speed reduction from the deadside to the end of the downwind leg and beyond, depending on aircraft type.
We were taught them at BFTS on JPs, using 45 to 60 degrees AoB and airbrakes out until rolling out on the d/w leg. The problem is judging when and where to begin "breaking" to fit into a busy circuit so as not to cut anyone else up.
ShyT