Hmmm… The r2e that would be in $PATH would have no link whatsoever with the one enabled by the service as far as I remember, so it would sound like a footgun, but the manpage is a point.

Do you think it'd be reasonable to split the rss2email derivation to have rss2email.man, and only include the .man in systemPackages? This way it wouldn't be as much of a trap

What do you mean? it’s the same package as in the ExecStart?

Indeed, what I mean is doing r2e run won't actually run rss2email, because it'd operate as a different user -- so the r2e in $PATH would have no way to interoperate with the services.rss2email module -- contrarily to what I usually see with modules that make available something in systemPackages

Then I guess I just never noticed these services, and this is good to go :) my experience has been mostly with (systemd and) opensmtpd, where the *ctl command is installed -- I haven't noticed many other packages globally-installing packages, but if I just missed them, then that's all good!