I can confirm, I’ve tried flaxseed (based on this article and other ancedata) and while the seasoning came out really nice after 6 months or so it has started to flake and after a year it looks really bad.
Agreed. This article started a fad when it came out 10 years ago, and now everybody agrees flaxseed oil is a bad choice, "science-based" as this may claim to be.
How the heck do you get a thick enough layer to flake off?
For me, it all just came off when washing it, 6 months or a year after seasoning. The sponge was filled with black flecks. Seems like once you get a defect in the surface, it fails catastrophically. With more traditional seasoning oils, the seasoning gets thinner gradually as it's abraded away.