I only extend the warranty for something that is likely to have a problem and where the fix is likely to be a lot more expensive than the extended warranty cost by a factor of 2 or more.
Labor to replace one of these units is minimal and my new AC sold for $900 and I bought it and had it installed for a lot less than that amount. These also seem to be rarely a problem.
Different with a fridge where the controller boards often are the point of failure and the labor and parts will be over $600.
In general extended warranties provide a profit margin of 90% or more. That is not to say that they are all bad all the time.