They have been here in the Netherlands for decades so feels odd to see it is such a novelty in California. Happy to see they work there too!
That's not light traffic, that's basically no traffic. I don't think anyone bothers to build a roundabout for such intersection.
Roundabouts are for light to moderate traffic scenarios. Their main benefit is that they get drivers to slow down, which vastly reduces number of accidents and fatalities on the intersection. The effect on throughput is secondary, as the intersection was not congested anyway.