Last I checked they weren't really any quieter than their competitors at the same airflow and pressure (which is a little subjective because your curve will never match perfectly). They do have a really low number on their specs because they have a really low max RPM, but that's not really relevant when you can just lower the speed of other fans.

They're still really good fans, but a lot of this is just marketing.

At max power the Noctua NF-A12x25 has 56 CFM and 2.3 mmAq for 31dBA [1]. At 70% the Artic A12 Pro is 56 CFM, 4.3 mmAq, and 31dBA [2]. At 60% the Asus ProArt PF120 is 61 CFM, 2.6 mmAq, and 30 dBA [3].

Note that the ProArt is a bit thicker (25 vs 30 mm) and all these dBA numbers are almost certainly unobstructed airflow. The Noctua is certainly good, but it's literally over 5× the price of the Artic.

[1]: https://www.cybenetics.com/evaluations/fans/4/

[2]: https://www.cybenetics.com/evaluations/fans/175/

[3]: https://www.cybenetics.com/evaluations/fans/229/