Your first comment is accurate, no one uses turn signals in any of the ones I use on a daily basis either, but that doesn't make them inefficient. In fact I think it keeps everyone on the defensive, and makes them pay more attention before entering.

But as I said in an earlier comment, the reason they kind of suck in the US is we don't seem to do them right.

* A very wide circle (350ft/100m minimum) with 3 lanes

* Each entrance and exit has 2 lanes.

* The outside lane of the circle directly connects the outside entrance with the "first" exit.

* The middle lane of the circle and the inside lane of the entrance allows you to exit at ANY of the exits

* The far inside lane of the circle exits nowhere without a lane change, but allows you to bypass an exit that might be backed up due to traffic.