The only con I've been able to find is a) it only works if you remember to start shopping at smile.amazon.com, and b) the sign up process funnels customers to p

The only con I've been able to find is a) it only works if you remember to start shopping at smile.amazon.com, and b) the sign up process funnels customers to picking the larger and already well-known non-profits -- it is possible to pick any registered 501c3, but find and setting the smaller non-profit is fiddly and requires special knowledge (tax ID number) to complete.