The Masimo RAD-57 is a nice device.
Besides COHb, it can come with the option of MetHb (methemoglobin) which will also skew you SpO2 reading. Methemoglobinemia may need to be considered especially when exposed to oxidizing medications and other chemicals, including nitrates, nitrites, prilocaine and lidocaine, nitric oxide, and aniline dyes.
Unlike CO, skin discoloration can occur in patients who are not anemic with as little as 1.5 g/dL, or approximately 10% of Hb showing MetHb. If this discoloration does not disappear with 100% O2, provided there is not a significant pulmonary history as a cause for cyanosis, it would be wise to thoroughly check their medications, question recent endoscopy or bronchoscopy procedures and look for open or spilled chemicals or exposure.
If it is used for potentially known situations like fire rehab and northern homes then you may not need the additional MetHb. If it is used for general N/V/SOB, then yes it may be needed.
The question to ask would be how much is it going to change what you do?