you can now build full system images (and blobfree builds too) of B2G OS for the ZTE Open C FR and the ZTE Open C EU (Ebay).
You will require an Open C phone rooted using the official tool available from ZTE support page for the Open C [FR] for the FR variant, or the equivalent tool for the Open C EU.
To build, follow the usual steps, just use:
to build for the FR variant, or
to build for the EU variant.