Fridges, freezers and the combination are about the most reliable domestic appliances there are - unless one buys a mickey-mouse brand - which you haven't. That is why it costs relatively little to purchase an extended warranty.
All there is to go wrong in a fridge/freezer is one (or two) electric motors with compressors attached to the shaft(s). Not like your average washing m/c with their multiple motors, valves, timers etc.
For peace of mind you may wish to do this, but I reckon that are poor value for money.
My beer fridge (kept in the garage) has been going since 1983 - it was once our domestic fridge.