I'd say for the oxymeter it depends on what you want it for. If your health depends on it, yes spend more for a good one. If it's just for general interest the cheaper ones will likely be "good enough".

For batteries, generally true. Except the Kirkland non-rechargeable packs are very good batteries and good value too. Not that I often need non-rechargable. Just for those few devices that are not happy with the lower voltage of rechargeable batteries.

Otherwise, definitely a good list. I'd also say in general for electronics, be very wary of Chinese brands you've totally never heard of selling items for less than half the price a reputable brand sells the same thing for. They are generally putting fake CE/FCC labels onto devices that are definitely not certified and will almost certainly be underrated for the requirement in a best case scenario. I am currently especially suspicious of the 100w+ PD supplies that are ridiculously cheap compared to known brands for the same rating.