Well any car can have major expensive repairs.
The profit to the salesman and company is usually over 50%. So for every $1,000 you spend the insurance company has less than $500 to pay for repairs or they will loose money, something insurance companies do not do. Some peop;le will get nothing back and some will get a lot more than they pay. Most will get far less. In addition you need to keep in mind that the insurer has worded it to eliminate as many expensive things as they can.
Remember that the seller is out to make money and they get to write the rules and set the price. They are not going to sell them at a loss so one way or another they are going to have you pay more than they will pay out.
Would you gamble with a car dealer who gets to set all the rules and knows all the odds?
Your decision has to do with the value of the piece of mind it gives you. If that is worth the cost then buy it. Don't expect it to cover everything however, most are written to keep cost down and exempt what they know will cost them money.
Good Luck