Service contracts are sold on fear. The pitch pictures a transmission failing on a highway with no money in the account. Sometimes that picture is yours. Often it is not, and the first job is to tell which situation you are in, because a contract answers only one kind of problem.
The problem has three parts
A service contract is a prepaid promise to pay some repair costs on named parts for a set period or mileage, after the factory promise has ended. So the problem it addresses has three parts: the car is past its manufacturer coverage, a covered part can fail, and the repair would land on you at a bad time. Remove any one part and the case for a contract gets weaker.
Ask whether the car is still under factory coverage
Look up the remaining factory warranty for the car you actually drive, not the one in the brochure. If the manufacturer still covers the powertrain for a long stretch, a contract buys protection for a period you already have. Read the factory terms in your owner's booklet and note the age and mileage limits. This overlap is the first thing to check, and it costs you nothing to find out.
Ask how you would pay a large repair
Picture the worst common failure on your car, then write down how you would pay for it within a week. If the honest answer is a credit line you would hate to use, or a repair you would have to skip, the problem is real for you. If you could pay from savings without strain, the contract is replacing a cash reserve you already have, and you should weigh that trade openly.
Ask how long you will keep the car
A contract only pays off if you keep the car through the period you are buying. Be honest about your plans. If you expect to sell soon, you are buying protection you may never use, and the cancellation terms become the real product. Check how refunds are figured before you assume anything about them.
Where to find the published figures
This site publishes the terms of named providers in its own tables, including money-back periods and waiting periods. Use those tables to compare providers, not to decide whether you need a contract at all. Only you can judge whether one unplanned repair would hurt your household. A contract is one answer to that question, and not the only one. You can start with the providers listed by money-back period once you have decided the problem is real.