Larry,

This unit can meet some of the testing requirements of NFPA 99.

I believe the manufacturer markets this for existing facilities, that perform ongoing periodic testing of their outlets/inlets.

This unit has limitations.

To my knowledge, it can test operational flow, and gas concentration.

At one time I had heard that it only utilized an oxygen analyzer, so it could not test gas concentration for nitrous oxide and carbon dioxide. This may have changed with newer models. I have not seen one recently.

Knowing its limitations, will help you understand if it meets NFPA 99 code requirements or not.

Sounds like it uses a "Facebook" algorithm to differentiate.  First O2% (probably >95% = O2, <95% = other gas).  Then, it looks at system pressure (which is why it went from N2O to N2 when you increased pressure).  The question is how does it differentiate between N2O and CO2???  Since it is for "annual / existing facility" testing, it must assume that no cross connections exist (since it should have been previously verified).  If they can't tell you how the technology works, it is suspect out of the box...in my humble opinion!  We should be able to validate its function in order to make sure our testing procedures address any potential equipment constraints.