For those who might be interested, heres a snippet from a Mistral review written by Charles Hood in the March 2005 issue of Dive magazine (I think it explains quite clearly the differences between the new Mistral Twin-hose and the old):
The new Mistral has four low- and one high-pressure port so that the diver can connect the full range of peripheral equipment such as an octopus, submersible pressure gauge, BC and drysuit inflators. The Mistral first stage comes with either a 232-bar yoke fitting, a DIN 300-bar fitting or with the new nitrox/O2 M26 x 2 to allow for any configuration. Its first stage is based on the existing Titan. Its operating principle is the same as that of a single-hose regulator. Unlike the original twin-hose regulator, the flow of air is delivered in two stepsfrom the first stage and then the second stage. To get around European regulations, the first and second stage, despite being mounted on the tank, are connected by an intermediate hose and to make matters even worse you are given a choice of a shorter hose for warm-water use and a longer one for cold water. The logic for this is that in an ordinary single-hose regulator the hose has to be longer for the air to warm up between first and second stage. Personally, I think they should have tried to find a way to integrate them as one unit, even if this means they cant be used below 10C.
The new Mistral is approved for cold-water use and has passed the EN250, EN 144-3 and EN 13949 standards, which among other things required a breathing effort below three joules per litre at a depth of 50m with a supply pressure of 50 bar. Aqualungs own test divers have taken it under ice and have shown that the Mistral resists freezing, even under such extreme conditions as a forced extended free-flow. This is because the Mistral has both first and second stages fitted with environmental protection. Cold water never comes into contact with the moving parts.