The archive of blacksheep maintained at

 https://klubnl.pl/rsgb_lf_group-archives/html/rsgb_lf_group/

works well, is at least partially indexed by Google, and the
archive is downloadable in the long-established and well known
mbox format.

The old Yahoo group and its migration to groups.io does not
have a public archive, therefore messages posted are lost
forever.   Without an archive, there is no enduring history
of LF and VLF developments.

When blacksheep eventually fails, the RSGB LF group will at that
moment disappear from history unless a new non-secret group is
created on groups.io

Apart from the unwarranted secrecy, groups.io provides an ideal
platform for a forum, there are no privacy or security issues.

--
Paul Nicholson
--