Originally Posted by Kacee

The only reason to consider buying and upgrading is if you really really want the miles to get you closer to gold. Otherwise, a saver award ticket will be a much better choice. You will have much more flexibility on routing and carriers. On the other hand, the co-pay on a miles upgrade will be significant (likely $1000+ RT), you will only be able to upgrade flights on UA metal, and you will have much less routing flexibility in terms of stopovers, etc.