all traffic is known (radio contact or PPR by telephone)
2. all traffic is turning in the same direction
I don't see why traffic has to turn in the same direction. If one pilot wants to do a LH circuit for 25 and I decide it is in my best interest to do a RH circuit for 7 (assuming this is allowable) then there easily could be a conflict anyway. The Radio operator has no authority to give directions, but can only offer advice and the PIC is responsible to the safety of the flight.
Its nice to have an operator to pass weather info etc.., but at the end of the day, it is the pilots decision how to proceed and therefore an ATZ is meaningless at an uncontrolled field - and probably just adds to confusion and a false sense of security. Unlicensed fields don't have them.
Either get rid of them, or give Radio / FISO operators the authority to issue "clearances" (and make them responsible) within their ATZ. I'd be happy with that.
cheers