A font editor can feel smooth while producing files that behave differently in applications. For a Birdfont comparison, draw a small set of glyphs with curves, accented characters, and a few kerning pairs. Export a font and install it on a separate test machine.
Check spacing at multiple sizes and in a browser, document editor, and design tool. Look for missing outlines, broken accents, naming problems, or inconsistent kerning. If the font will be distributed, also examine the license terms and what metadata the editor writes. Keep the editable source and a known-good export so a later tool change does not strand the design.
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