Politely disagree. M-disc for BD-Rs are still absolutely worth the money if you want to properly archive something. NIST has agreed that the archival lifetime of a M-Disc BD-R is 100+ years.
You have to be careful with normal BD-Rs because there are two different types of recording material on the market: High to Low and Low to High (LTH). You want to stay away from BD-R LTH discs as their longevity isn’t as good as the High to Low discs.
Sony will cut around 250 jobs from the recordable media business manufacturing hub and will gradually cease production of optical discs, including Blu-ray discs. ( mainichi.jp )