Well, I've lived in The Netherlands and I would say that the extra complexity of the bicycle path (which generally leads to a bicycle roundabout outside the car one) does push for having to help drivers a bit extra in the absence of traffic signs managing the thing (since anybody exiting the roundabout still has to give way to bicycles).

That said, even in my own native Portugal, were maybe 9 out of 10 of all drivers do not properly and reliably use the direction indicators (from personal experience I would say the quality of driving here is one of, if not THE, worst in Europe) roundabouts are all over the place, clearly help and don't seem to be any more accident prone than regular T and X junctions.