Best language learning app on here! Wyder’s method is powerful, in the mathematical sense of fundamental & generalisable.
Starting with training on the given language’s IPA with a minimum of English allows learners to quickly assimilate phonological intuition, which then makes remembering morphology as simple as sounding words out.
Glad they’re working to expand the instruction on syntax (grammar), as it is the primary deficit in spaced-repetition generally.
Combining FluentForever with Anki, Duolingo, a good easy reader, audiobooks/podcasts in target language, and a reference grammar will go a long way quickly toward achieving at least B1-2 fluency.
eg For German, am using Fluent Forever with Duolingo, good Anki decks like German IPA (with audio, IPA, articulatory anatomy diagrams), Steinhauer’s “Easy German Reader” (see also André Klein, Olly Richards, Dover Dual Language), and watching series’ like “Dark” & “Babylon Berlin” on Netflix first with English subtitles, second with German subtitles, finally with no subtitles.
Just grabbed Wyder’s book, which is for any language, but if you’re also doing German:
Mary Grantham O’Brien & Sarah M. B. Fagan, “German Phonetics and Phonology”
Christopher Hall, “Modern German Pronunciation”
April Wilson, “German Quickly: A Grammar for Reading German”