I cannot explain why anyone on reddit says anything in particular. I can tell you that the redemption rate United offers for paying the annual fee is better than the 1 cant per mile (or less) they offer in some other situations. Whether or not the miles are worth more than $550 depends upon what you can use them for. I can tell you that the best ratio you can achieve between cash prices and award miles needed would be for one-way international flights in business or first class. However, these flights (a) are not always available; (b) require a lot of miles and (c) only do you any good if you happen to want or need to travel there. At one time, the absolute best value in the system was Thai Airways first class from Bangkok to Sydney or Melbourne. However, I never took it, because there never happened to be a time that I was in Southeast Asia and needed to get to southeastern Australia.

The *A lounges wouldn't allow you to use them on arrival. Also, you must be flying on a same-day *A flight -- you cannot enter the Untied Club with a Delta ticket, even if you're a United Club member. However, given those constraints, you may use the club with your membership, subject to the club rules.