The article appears to imply that the smaller ones are better, so on that note, large intersections between 6 or 8 lane boulevards are right out for conversion.
Smaller ones are indeed better.
Along as they aren’t sized for go carts.
Yes, smaller is better. 2 lanes max. I don’t think there should be any roundabouts 3 lanes or more. If you have 3 lanes or more, just put in a traffic signal.