V-tail:
But most airfields in UK have radio, and we don't need to fly over a signal square to get our landing info. In my opinion a join at circuit height on the extended downwind [or on base leg] is a lot safer than the OHJ
You've hit the nail on the head of where the OHJ falls down. It's where people think they know better and muscle in on the circuit in the way that suits them, while others try to stick by the book and fly an OHJ. I'm heartily fed up of thoughtless and selfish PPLs barrelling into the circuit on base or downwind or god save us "long final" while I've got a student on a circuit detail. You're right most airfields have radio. So when they add at the end of the airfield info "the circuit is active", please spare a thought for those of us who are already in the circuit.
And I don't agree with you about OHJ only being of use at remote non-radio strips. In my view OHJs are pointless there because they won't have a signals square, might not have a windsock, and almost certainly won't have other traffic. OHJs are the best way of ordering joining traffic; their original purpose of enabling you to read the signals square is now redundant.
NS