The best one on the market: the Dräger 'Labor' reducer as used with the DM 220 Hard Hat Equipment. Myself I use 2 of these reducers when diving my Friedrich Flohr Copper Helmet with Regulator Backpack: one for the regulator and one for the bypass which is connected to a USN MK5 Air Valve. I have several of these in stock, all officially serviced and then stored: in 'new condition'. We also sell the Air Hoses to fit this system (I use those for hard hat diving myself as well: much lighter then the good old ones). The original price tag is still attached: €711,35. I sell them for €199,- each plus shipping.
Dräger Reducer for the DM 220 Hard Hat Equipment