I have roughly fourish separate monitoring systems for Appointment Reminder. DMS is the one which is least tied to me, so I use it for Tarsnap (the most critical thing about AR that can fail "quietly") and as the fourthish line of defense for the core AR functionality.
(This may be slightly overbuilt, but I felt it justified to get peace of mind, given AR's fair degree of importance to customers/myself and the enterprise-y customer base. In particular, I would not have been happy with any monitoring solution which would fail if I lost network connectivity at the data center.)
$15 a month is far below my care floor for making sure that my backups are working and that I do not get sued into bits.
