Looking to promote someone...

Cherche can be utilized extremely well in a fliers team, focusing on sheer damage output, preferably during the PP.

I wouldn't invest much into Frederick, unless you like him as a character.

Cherche is always a solid nuke with a brave Axe and death blow. With an attack boon she will be initiating with 55Atk, 61 with hone fliers.

If nobody else is using it, slap the Heavy Blade 3 seal on her for nearly guaranteed moonbow on second hit

i can say cherche is amazing unit and easy to 10+. atk+ hp- death blow, desperation and brash assult seal is what i run and its very fun to quad. frederick is a luna fodder for me even if he has perfect ivs

Cherche has one of the highest atk in the game, so she's definitely a worthwhile investment. I value f2p units with Hammer because of how goddamn common armor emblem is in arena assault, and I've upgraded both Fred and Cherche as well as Bartre as specific anti-armor units

Cherche is certainly worth it but as she's a common 3-4* a 4* merge may be better if you can source a 5* weapon, either Hammer+ or Brave Axe+.