Lower

Oximeter use infra red light, one side beam thru finger and capture on the other side

Smartphones that beam white light and measure from camera very poor accuracy. Samsung use red light slightly better only..

Then smartwatches beam on wrist instead of finger also poor

Those cheap mass oximeter may have reliability issues but its accuracy is likely much better than phones

So if wana grade them

A- medical oximeter
B- reputable oximeter (medisana etc)
C- mass oximeter (china made etc)
D- smartphone red light
E- smartphone white light/ smartwatches