The duo mount is a good idea but:
The mounting screws to the barrel were short and did not provide enough grip/strength to the barrel, screws would shear off.
Because you can't adjust the distance between the rings some people can't set the scope at a proper distance to thier face. Especially on rifles.
Standard weaver style bases, when used on heavy and tappered barrels, leave about a half an inch of overhang where the mount extends over the taper on the barrel.
SSK makes nice flush fitting mounts that have 6 screws to keep the base on any caliber that gives off some recoil.