Really... this one wouldn't be an alternative?
Available on Crewfit 275N, 150N and Freedom
The Hammar Inflator gives exellent protection from random activation caused by moisture, rain or wave splash. This is achieved by protecting the water sensitive element with a hydrostatic valve, which operates when submerged in over 10cmof water and, depending upon the Lifejacket style, held there for between 2 to 3 seconds.
Hammar works on water pressure, only operating when submerged in 10cm of salt or fresh water.
No accidentalk inflation, even in extreme conditions.
Cylinder is mounted on the inside of the Lifejacket inflation chamber.
Re-arming instructions and key provided with each Re-arming Pack.
Can also be inflated as manual version or orally.
There's the link from above.... It appears to be a European brand but perhaps still an option to the Mustang.