They are smaller (lighter) since the cores (I think) are wound from grain-oriented steel. They should be less expensive as they are not necessarily layer wound with interleaving, but they are not (less expensive), at least locally. There is also the blurb that they have less leakage field - that is technically true, but not necessarily of practical implication. The round form can be more difficult to accomodate than a "block" form. (When having local winders, one can shape a narrow format using a thick stack, which can be convenient. With a toroid one is tied down to l x b x h.)