https://www.gwern.net/DNB-FAQ contains a rather extensive review of this study and its follow-ups, critiques, etc, and comes to the conclusion that Dual n-Back training probably doesn't work to improve fluid intelligence.
That's quite a leap there. There is no contradiction between thinking IQ tests work and thinking that DNB increases IQ; I thought it did, and it was a bitter experience learning first-hand how exactly the Replication Crisis works.
If you think I am an unreliable source, why don't you look at the other meta-analyses like Melby-Lervåg, or Sala? Or look at the criticisms made by researchers like Redick whose experiments turned out to be nulls? (Redick's most recent comment on DNB is titled "The Hype Cycle of Working Memory Training" https://journals.sagepub.com/eprint/U8YNVXKM5SKF6ZY9TQBR/ful... , so you can probably guess what he thinks of DNB now.) Or look at what the field thinks in recent studies - assuming you can find any recent DNB/IQ studies, as everyone has realized that it doesn't do anything.
