The late British gun guru (and engineer) Gough Thomas thought highly of "fretted" barrels. From his "Gun Book":

"With resleeving now thoroughly established, it seems remarkable that no British firm has adopted the fretted barrel, with its possibilities for combining greater strength with a reduction in the cost of producing double guns." He continues the subject for a long paragraph.

Manufrance also used fretted barrels, going back quite some time. Most of their "Robust" guns have the very visible "step" between the monobloc and the tubes. In fact, at least in the States, if you see a gun with that "step", I'd say there's at least a 90% chance that it's a Robust.