Cosmic Stainless Steel Mass flow meters vs cheap Thermal Mass flow meters.
Flow meters built with cheap thermal mass flow sensors have a tendency to get contaminated, and deteriorate in performance very fast.
They could need periodic replacement (which may be a source of regular revenue to the manufacturer) but definitely a burden on you adding to your cost of ownership...
Such sensors are most likely specified for flow rates of dry air only, but 'adopted' for other gases (because the density of the gas is never measured in the system), the mass flow rate they measure is just an estimate.
Ultimately you end up paying huge replacement costs over the years, and you are never sure of the flow results.