If you haven’t completed the purchase, I think adding it into the contract is a good idea. We had one and the first summer after buying our house, the central air unit died. We found out that the contractor bought a terrible quality unit and we ended up getting a name brand new one (worth a few thousand dollars) and a new warranty on that specific unit through the manufacturer. We were without air for three weeks and it required MANY phone calls back and forth but in the end it got us a new, quality unit that would have been very expensive.
We renewed it and when the Amana dishwasher mother board died earlier this year (a few months outside of the manufacture’s warranty) they fixed it for the one-time fee to come out ($60). We now have a leak with the water line in the Whirlpool fridge (again about 9 months out of warranty) and they will be coming out again.
They are frustrating to deal with, and can require phone calls to get things done but in the first two years we have owned our home (a flip from a reputable contractor) we have gotten our money’s worth and will probably renew one more year. We use American Home Shield.