I've been using the SF800 from Swissflow lately to measure propane flow rate. It works well once you realize that the red wire is ground not positive supply. It uses BSP threads which are slightly inconvenient as well. The version I'm using has a fiber reinforced plastic housing and is rated for working pressures up to 230 psi. They have a metal bodied version rated up to 3600 psi that I plan to use with N2O.
Instead of using a steel rotor and a hall effect sensor, this meter has a plastic rotor with an IR emitter/collector pair. It outputs a nice square wave pulse with frequency proportional to flow rate. My DAQ board (from Measurement Computing) has a counter input which can be configured to measure frequency so interfacing to the existing DAQ software is quite simple.