Just be careful what class that you book into if the chance of an upgrade is important to you:

# Upgradeable Booking Classes fares: This upgrade may be used on United Business booking classes (C, D) and United Economy booking classes (Y, B, E, M, U, H, Q, V, W, S, T, K, L) for travel in Region 1. This upgrade may be used on United Business booking classes (C, D) and United Economy booking classes fares (Y, B, E, M, U, H, Q, V, W) for travel in Region 2.