Pretty much all home pulse ox sensors will be about the same in quality for the price. I've used the Walgreens brand for years and never had an issue. Try to get one with a hinge that opens (most are) rather than a "slide in" kind. Easier to clean.
Keep in mind they are only as good as their ability to pick up a good pulse, so if your hands are cold put them under a warm blanket and try multiple fingers. Very easy to get an artificial number. Always verify the pulse rate is the same as what you can feel on your wrist. Most will have pulse waves you can watch to match. In general if the pulse wave is strong on the screen and the pulse rate is accurate, the listed o2 sat will be accurate.