Read the fine print, most require you to do maintenance on their schedule, for example you need to change the oil every 3000 miles or every 6 months. Miss that by even one day and they will deny a repair of a covered appliance because you didn't do the maintenance even though a oil change has nothing to do with that appliance breaking down.
Use the manufactures warranty until it expires then if you want, buy the extended warranty from an individual company for another 5 years or so.
If you buy now, keep exact records of all maintenance done with exact dates and millage.