add an enable/disable button

Is this still un-implemented?

I'd like to know whether this module is going to send out notifications immediately upon enabling, or whether that's configurable.

+1 for this, and for installing in Off state. It can be worrisome to enable a module and be unsure if it's about to email a lot of users.

I'd like to be able to keep the module enabled but turn off reminders while playing with site/module/user settings.

This would also fit in with #355648: add functionallity to user edit page? to allow for manual sending, but keep automated off.

just happened to me: enabled, forgot to check when next cron was to run. module sent default message while i was typing to modify the email message.
my fault yes, should have checked cron time. but not a good reflection on the module as far as usability.

Committed to d7 branch. Setting as to be ported to d6 branch at some future point.