You want my honest opinion?
It's a set of standards on how a company should be run written by a bunch of bureaucrats who have never run a company but think filling out a bunch of forms and writing down a bunch of buzz words somehow assures you are doing a good job at it. I told that to the guy in charge of ISO certification for a company once who was blathering about how great he was. If looks could kill.
ISO is a Switzerland based non-governmental organization, NGO, made up of "members" which are in fact just other standards bodies within 150+ nations. The US member is ANSI. All these members vote and run the place, which is great if we're designing file formats and such and publishing them as "standards" so people can be compatible.
Where it fails is when they publish standards for something as intangible and subjective as best business practices. As a guideline ISO 9001 is fine, but so are any number of basic outlines published by myriad academics.
where it hits the fan is if you are committed to quality or not, and no amount of paperwork and certification and words can make it so.
It ends up being like a college degree. There are brilliant lawyers and horrid lawyers both with the same degree from the same school hanging on their wall. All it proves is they did the work to get the paper, it tells you nothing about how much they really understood it and how they can apply it in practice to help you. Likewise ISO 9001 can tell you they filled out the paperwork and paid the fees and got the certification, but it can't really tell you if they company is well run and managed and committed to quality any more than a law degree tells you a person is a great or bad lawyer.
Like school, you can go through the process and get a lot out of it or come out with the same degree having skated by and learned nothing. No amount of paperwork will stop bad management decisions or make people care about quality who don't in their souls worry about quality.
It's an admirable goal, but in the end Taurus will either turn out quality guns or they won't, and the market will make that determination, not a group of people who by and large have never turned a lathe or fired a gun.
Having or not having ISO "certification" IMO tells you nothing about the company of use when making a purchase decision. It tells me they are probably contracting with someone who requires it, which is the "racket" part referred to in M29's excellent post.