We purchased a pre-paid service plan over a year ago when we had a/c problems that Mowery fixed for us.
They send out a reminder card that it is time for the visit.
Technician fully tested and checked all components of our heating and cooling system and left us with details about what type of things we needed to do to keep the system running efficiently.

Went extremely well.  Tech was very thorough.  There were no “surprise” costs that came up or a surprise repair that they found to do.