I got Hokage Tsunade from crazy slot machine a long time ago after recharging $5 for monthly card (that was the only time game ever gave me anything nice), so I never knew how long/much it cost to piece her together. But about her usage, she's still among one of the best healers in the game, but she's pretty situational. What Hokage Tsunade have over Sannin War/Sannin Era Tsunade is 9-12 unit heals, which if you stack earth shield+2 other Hokage Tsunade in gnw against opponents who don't have way too much BP advantage over you, can make your opponents hate you very very much. Otherwise, Hokage Tsunade is also decent in Bonds and ranked battle lineup. She's also one of the option for perma-chaos variations, since her passives allows better healing/surviability. However, she's weak against constant focus and too much cc/debuff stacked. Full bt Sannin war Tsunade is better in general 1v1 environment, and I don't have enough experience on Sannin Era Tsunade to comment on her. So is she a nice ninja to have? Yes. Is she absolutely necessary? Well, that depends on what you want her for.