FYI
The Onyx will work for personal use but it's designed for patient care; that is, for it to be placed on a patient finger and then read by the person standing in front of the patient; so the numbers will look upside-down to you unless you curl your finger so that you can read it or just read it upside down. Being that it's certified for medical use, it's also more expensive than the consumer version.
The GO2 on the other hand is designed for home\personal use so the display faces the reader, and though it uses the same technology, is much less expensive.
http://www.nonin.com/go2/
http://www.nonin.com/
*I think you can get the GO2 for even less through Amazon, though verify the seller because there are Chinese knockoff's hitting the market.
**Also, if you have health insurance, check with your physician as it may be a covered product (depending on your carrier).
.