Military (timed) circuits always seemed very sensible to me as they tended to take account of hugely different aircraft performance - you could be doing (6 minute?) circuits in a chipmunk at the same time as someone else learning to fly a Hawk without there being any issues. Sadly most airifelds are surrounded by Nimbys, who seem insist on a geographical noise-sensitive acceptable route. This precludes differing performance being able to fly without something else giving. If it seems necessary to extend outside the ATZ then surely something has gone wrong and someone needs to accept that they have to give up and try again.