Unido plays on a synthetic pitch which most teams struggle to adjust to. In the last round of this competition, they beat Pachuca pretty handily, 4-1. Cruz Azul took quite a few reserves down to Panama.
It looks like the Mexican teams aren't taking this competition very seriously. No Mexican team won their first leg yet, and most of them have sent reserve teams so they can prepare for their league games this weekend.
(I wasn't originially going to play this, but Unido is sitting at Pick (+110) right now. Might make a small wager on the Panama side)