FYI, not sure if their final product will have an external antenna but the prototype Z-Wave Controller USB radio adapter stick that Nabu Casa (Uwe and Dominic) has tested does have an external antenna, see picture of their Z-Wave Controller USB dongle prototype in green color with external antenna in the blog post → Z-Wave is not dead - Home Assistant
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Left: Dominic, slightly jetlagged, with our stick prototype (green). Right: DrZWave with the controller reference design (purple). Background: Uwe, 0.7 miles away.