ESPHome reduces the download and wait for a first nRF52 firmware build by fetching only the parts of the Nordic software kit that the configuration needs. Interrupted downloads can resume instead of starting again, and the log shows their progress.
In J. Nick Koston’s test of a basic ItsyBitsy configuration, setup and the first build took 99 seconds instead of 372, with the kit using 964 MB rather than 2.2 GB. The test started with an empty kit directory but an installed Python environment and compiler; both builds produced identical firmware. Authors of external components needing extra Nordic projects must declare them explicitly.