Please see my fork of Mona Sans which has an updated config.yaml (saves to /googlefonts, ital axis instead of slnt).
The new ital splitter works great, in some ways better than plain varlib.instancer in how it handles the fvar instances.
But Mona Sans now shows two ital axes in STAT, which I assume is a bug.
Both Italic and Roman show a similar behaviour, except that the Italic says Italic in the first screenshot instead of (Roman)

