its nice to upgrade flight 300+ days in advance, and not wait till 7 days like SE do, however clearly AC program works for flyers who have someone else paying for high fare class flights. Also Polaris lounges are spectacular, and Signature all of a sudden because pretty bla.
United has 60 business class seats on its 777-300. AC has 20-44? depending on the plane? however its going to be at least another year for all 777 and 767 to get the Polaris seats so that's a big plus for AC flyers. However the Polaris seats are a lot nicer than AC pods.