The Trieste was the last of the Voit double hose regulators.  It was probably the only design that Voit made that was not all or in part designed or made by US Divers.  It is a very elegant design, but looses some mechanical advantage by using a small diaphragm.  This regulator also had the advantage of several ports for submersible pressure gauge, octopus, and auto inflator.  This regulator was prized by many and considered by many the best breather that Voit made.