The simulation technique [1] currently used by the Firefox / Chrome dev tools is reasonable, so it's definitely much better than not checking for color vision deficiency accessibility at all. Ideally, color should only be used for progressive enhancement; if your UI can be used in grayscale, it's probably fine.
However, the method originally used by both browsers, which is also used by some other tools, had no scientific provenance and produced clearly incorrect results, so one needs to be careful about this sort of thing in general.
However, the method originally used by both browsers, which is also used by some other tools, had no scientific provenance and produced clearly incorrect results, so one needs to be careful about this sort of thing in general.
[1] https://doi.org/10.1109/TVCG.2009.113