The card costs 1, so 2 "equivalent cards" as some like to count for 3 cards AND you need to fill the Team-up condition while neither the Gamora ally nor the Nebula ally gives you a good reason to keep them alive (contrary to the Rocket Raccoon and Groot allies).

• Positive card count of +1 (3 cards vs 2ER).
• Quite more decent for when both players are Nebula and Gamora. Valid condition even if your parner is in alter-ego.
• serves as subtitute (for you both cannot play your identity specific ally)
• In line for what makes Nick Fury powerful: cycling the hand in search for more options

Overall, we had good times using it everytime It appears in our hand. Probably way less appealing when going to team-up with your identity-specific ally (both are made to not staying around for many turns so the window of opportunity is scarce).