Wim Hof is an individual case study that has done research in this area, and other related phenomena (breathing and autonomous response control)[1]

Not sure it's any more or less "bro science" then this article, but it's interesting and relevant enough to be worth talking about here I think.

[1] https://www.radboudumc.nl/Research/Pages/PNASIceman.aspx

I read his book and started practicing several months ago. The other week I played in the ocean for 20 minutes and it didn't bother me at all. Checked the water temperature afterwards and it was 56 degrees.

I haven't started with his breathing exercise, just practice, attitude, and knowing what to expect count for a lot.