Me thinks you take the analogy to literally - so I will answer you in the same vain:
If one or more of your control surfaces is jammed, due to the "Home Depot" plug having come loose, no amount of gas monitoring will save you๐คฃ
"Besides, you should have a working CO monitor in any aircraft cabin to ensure you don't get accidentally poisoned by toxic fumes."
You betray yourself, in your absolute confidence/dependence on third parties to make decision about your homebuilt aircrafts servisabity - Monitors do not prevent poisoning or anything else. They inform (IF working correctly) & IF the pilot takes note/notices, of a potentially dangerous situaton -IF!!! the pilot is in a condition to ameliorate the situation, they may save themselves.
You could inform yourself about the quality of alternative parts but Noooo!, rather delegate this to a (usually) unknown person(s) who will issue you a piece of paper, inferring quality/suitability.
As always I support your right to make your own decisions in this area. However find your logic both wanting and now, apparently, inconsistent.๐คฃ๐