IMO seems that the certifications for this devices, especially for the ones used by medical stuff to decide things need to be better tested.
Other interesting point that I did not consider is you can have a device with an average error under a safe threshold but that gives a much above average error for some groups putting this groups at risk if the people using this devices are not warned about this issues.
It is a long article with many studies cited so I can't check all of those, IMO "the readings can be affected by skin tone" is not something that is sufficient for a medical device , what should a nurse or doctor do? There is no numeric value so what does that mean? is the device useless if you have dark sin or is it 2% wrong or as the article suggests the error is non linear and increases if you are suffering with low oxygen?
What I would do if I would sell this products is test with a few ranges of skin tones, and if needed have a switch on the device that you have to set for a certain level or if that is to expensive print instead of a number an interval and have the user trained to read that.
One of the off-brand meters was completely wrong (e.g. dangerous) for blacks, the other one was in between.