I have FlightCrew, but I'm not sure I am convinced of it's accuracy/effectiveness at the moment.
When I check the epub with FlightCrew it does point out some issues (mostly fonts not used and a few tags I was aware of). But what is bizarre is that it also indicates that the entire 'Fonts' directory, which already exists where Sigil puts it, also exists inside the 'Styles' directory (i.e. Styles/Fonts/), and it says the fonts are 'reachable but not present in the OPF'. There is certainly not a Fonts directory in the Styles directory..there is just the single 'template.css' file there.
Likewise, FlightCrew also says that every single one of the fonts does exist in the OPF but is 'not reachable'...when
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