No independent peer review has this tested. The circumstantial evidence for this is good but leads to expectations that indicates a limited applicability and a temporary, small effect. This is not a Nuremberg funnel.
The font was developed by people at a university at RMIT’s Behavioural Business Lab.
And the psychological base theory for this is called Levels-of-processing effect: the more the brain has to work, the slower you read and the more parts of the brain get activated facilitating chunking and clustering of memories. As such the theoretical foundation is rather solid, for a psychological theory.
Relevant papers pertaining to this theory and its application are:
Diemand-Yauman, C., Oppenheimer, D. M., & Vaughan, E. B. (2011): "Fortune favors the bold (and the Italicized): Effects of disfluency on educational outcomes", Cognition, 118(1), 111–115. (PDF)
Yue, C. L., Castel, A. D., & Bjork, R. A. (2013). "When disfluency is—and is not—a desirable difficulty: The influence of typeface clarity on metacognitive judgments and memory", Memory & Cognition, 41 (2), 229–241. (PDF)
Just one anecdote: I was to told to read my textbooks upside down to exploit that effect. Or with a mirror. I did that. I was slowed down by that.
It is claimed that
Sans Forgetica was tested against 400 Australian university students in laboratory and online experiments as well, so they’ve released it with some pretty solid evidence that it works. news.com.au
While the designers claim it did improve recall in testing the font, they themselves say it should still not be adopted universally:
About 400 university students have been involved in a study that found a small increase in the amount participants remembered – 57% of text written in Sans Forgetica compared with 50% in a plain Arial. […]
The font was designed with year 12 students cramming for exams in mind but could also be used to help people studying foreign languages and elderly people grappling with memory loss.
Blijlevens is keen to test the font in other contexts such as proofreading.
Banham, who has created about 20 fonts, said the typeface would be best used for short texts.
“God no, you wouldn’t want novels printed in it, it would probably induce a headache,” he said.
The font took about six months to develop and there were three different versions tested.
–– Guardian 2018: "Font of all knowledge? Researchers develop typeface they say can boost memory"
Unfortunately, Wikipedia already summarises the situation:
Sans Forgetica was spawned from a study of 96 Australian university students. An online experiment including 303 students followed. As of May 2019, no peer-reviewed research or data has been released that supports the assertions of the Sans Forgetica team.
The big problem in the room here is that it is still a standardised font and as such the small effect it did display in testing by the designers will diminish as people habituate to the initial difficulty.
Blackletter typefaces slow down most modern readers, but just like 100 years ago, this will speed up to normal levels once the new, formerly "difficult" shapes get so familiar that they can again be recognised by their 'word outlines' and skimming the text becomes possible again.
Reading upside down has no longer a discernible effect.
Visual Form Perception in Deficient and Normal Readers as a Function of Age and Orthographic-Linguistic Familiarity
Yet a typeface that relies on novelty to jolt the brain into absorption and retention also runs a fairly significant risk: What happens when the reader gets used to Sans Forgetica? The Mere Exposure effect is a psychological phenomenon whereby people express a preference for things simply because they are familiar. As readers become accustomed to Sans Forgetica’s initially odd appearance, grow more comfortable with it, and start reading it faster, will the retention rate of information decline? Will their brains simply adapt to the difficulties posed by the typeface in such a way as to eliminate the benefits?
Further long-term studies are the only way to determine whether this is likely. For now, the early results are encouraging, based as they are on solid principles of cognitive neuroscience. But while an increase of 7% in memory retention is measurable and real, it also doesn’t leave much room for decline within those results over time; in other words, if readers start to lose even 1% of retention every few months as they become accustomed to Sans Forgetica, soon the advantage is lost.
There are physical changes in the brain related to long term memory—a quantifiable difference between learning something quickly forgotten (like a phone number) and learning something that endures (like multiplication tables). A study investigating whether these brain changes actually take place after exposure to Sans Forgetica could shed additional light on the typeface’s effectiveness.
–– Angela Riechers: "Can “Bad” Type Design Help Readers Absorb and Remember Information?", December 10th, 2018.
And for the general theory from psychology, being as a field subject to replication crisis already, it sheds further doubt on the results for Sans Forgetica to read:
Prior research suggests that reducing font clarity can cause people to consider printed information more carefully. The most famous demonstration showed that participants were more likely to solve counterintuitive math problems when they were printed in hard-to-read font. However, after pooling data from that experiment with 16 attempts to replicate it, we find no effect on solution rates. We examine potential moderating variables, including cognitive ability, presentation format, and experimental setting, but we find no evidence of a disfluent font benefit under any conditions. More generally, though disfluent fonts slightly increase response times, we find little evidence that they activate analytic reasoning.
–– A Meyer et al.: "Disfluent fonts don't help people solve math problems", J Exp Psychol Gen. 2015 Apr;144(2):e16-30. doi: 10.1037/xge0000049.