He is perfect fit for them. They just needed a consistent goalscorer and he is a world class poacher these days still capable of very special moments like in Euros. Look at how many points Cavani won for them last year. The United fans are over the moon, haven't seen so much joy from them in a long time and its so annoying.
It also speaks volume that United don't even need him, but simply signed him because they couldn't afford to let City have him and eggs on their faces