@rqm I switched to it years ago and display today’s+tomorrow’s events in every shell (from ~/.mkshrc) as that’s the only way I don’t miss appointments left and right.
If you use the #MirBSD implementation, which has an extra "parse for export" flag with support for time-of-day, you can have one-way conversion to #iCalendar, which you can then read-only subscribe to from e.g. smartphones, or Bloatzilla Thunderbird.
Two-way is unwise, they hve vastly different "mightyness", e.g. recurrence is handled differently, and #BSD #calendar can do offsets from Easter and so (and MirBSD’s also from Advent), and #if and #include and cpp comments, etc. (which I use heavily in my private calendar, I even have a script to pre-fill with comment headings for the next year per calendar week).
https://evolvis.org/~tg/calendars/ has my public calendars in both formats (and links for subscribing to them through Google, for those who use that). The conversion cronjob runs nightly, as it uses "today" as startpoint for recurring events.