As TKB-408 requires 4 different Doll types in the Echelon, she’s not very usable. Her buffs aren’t bad, but making an overly mixed Echelon isn’t recommended for general use, and TKB-408 doesn’t bring anything that makes her appealing for Ranking.
As such, TKB-408 is not recommended.
Full analysis
TKB-408’s 4+ Doll type Crit Rate buff is flat, meaning she ends up at 50% Crit Rate with a PEQ (20% + 30%).