so the thing about these 3rd party warranties is.. some of them aren't that great (if) you ever have to use it. Theres some online stores that offer similar prices, or maybe slightly cheaper, and come with 3 year extended warranty via 3rd party. That might seem great on the surface, except some of these 3rd party warranty services are awful to work with. One of these is CPS, and I did some digging and read some not-so-encouraging testimonials by users trying to get a repair or replacement through them.
This bonus warranty offered by costco is through allstate, which I don't know much about other than it is probably handled by squaretrade b/c a few years ago allstate bought squaretrade. Checking the BBB page about allstate protection plan has a link to squaretrade website.