I use the CarbonDoser from Aquatic Marine. Rather than switching off and on an analog regulator, this small solenoid based system doses out CO2 "drops". No need for a drop checker with this. It's pricey though.
I have had the new co2art reg for a few months now that they gave me in place of their defective lower end dual stages & it's been working fine. The only thing is I don't think it's dual stage, but it does have a quality feel.