I think the answer is: It depends.
If you want an actual N95 grade mask then, yes, many of the KN95’s don’t meet the FDA standard. As covered in the article you linked, some still meet FDA requirements. I have not tested them.
@Snewkes covered in his post: “What are the most compact ones out there? As long as length & width are small enough to fit in a jeans back pocket (not actually where I intend to store them, just trying to give an idea of the size I have in mind), thinness is the top priority. I’m ok with the protection being somewhat lesser since I’d only use it in an emergency situation where I’d be getting out of the area as soon as possible, as long as it’s good enough to be worth carrying at all.”
Protection can be somewhat lesser, priority is thinness. In which case the fold in half KN95’s are suitable until you get to where ever you have your supplies. As a note, the link I included was only for demonstration purposes of what I was referring to – no idea if that link is an FDA okay’d brand/model.
But as to a certain mask being a good idea or a bad idea – it really does depend on your intended use. I find that long use (5+ hours) of the N95’s is very hard on the nasal passages, due to the seal formed by the mask and the pressure of the elastic to keep the seal in place. If you don’t mind that and you are driving away from a smoke filled area in a evacuation (wildfires for example) I would certainly put up with the pressure.
In a scenario where I have to be an area that has a contaminate such as chemical spill or abrasive disinfectants (real scenario for me) I will use an actual respirator with replaceable n100 filters. If the contaminate is heavier than that or the manufacturer recommends different gear for dealing with spills, then I wont go near it, another team will handle with proper gear.
But if I am simply required to wear a mask for government compliance regulations and health reasons where long wear and comfort are an issue, I will likely use something like a bicyclists breather-valve mask or the surgical style paper masks (I say style because there are many kinds of such a mask from those surgeons actually wear that will stop a spray of arterial blood all the way to what you see people wearing on the streets and in stores). A KN95 should be better than your bandana over the face style of mask.
So, depending on your use case, KN95 masks could be okay. Or they could really, really not be okay. But they will suit Snewkes’ requirements.