You have to ask yourself how many hours you are going to put on those engines before the extended warranty expires. I have seen a few analyses on consumer warranties and the only product where extended warranties work in favour of the consumer is on high end laptops. On every other product from cars to washing machines you were better off gambling. However, do you have the financial ability to deal with a catastrophic failure like a power head? What they sell is peace of mind, which is why we buy insurance in the first place.