Mustard wasn’t used to stop glare - it was to give the laser the ability to leave a mark on metal. In general 40W lasers cannot mark metal in any meaningful way. They can remove a coating, or interact with something else in a way that leaves a mark.
Cermark is great - but pricey.
The mustard/vinegar/paper towel experiments were successful on some.
I used LBT - but check out this video and you can see some direct comparisons: