Does anyone know of anything similar to (or a port of) GitHub - typesupply/glyph-nanny: A live report about potential drawing issues in your glyph. for GlyphsApp?
Got it, GitHub - jenskutilek/RedArrow-Glyphs: Glyphs users can also have red arrows and GitHub - mekkablue/ShowAngledHandles: Glyphs Plugin for highlighting BCPs which are not completely horizontal or vertical (menu item View > Show Angled Handles) 
Both available directly in the Plugin Manager.