Rivals Domain: HM Farming

Someone posted this link earlier and it seems pretty straightforward to execute. The only issue being that I don't have a Galeforce Cordelia.

With that in mind, I was wondering if I should promote my Cordelia and if it's worth the investment towards her? I've always wanted to promote her at some point but I've made my Draug a priority and neglected every other character. But if I were to promote her, I could easily HM farm since she seems like the most used unit.

She would need 20k feathers for 5 star. And another 20k to promote a Hana for LnD3. She's +Spd, -Res and I was planning on running her typical Brave Lance/QP/Galeforce.

What's everyone thoughts?

https://www.reddit.com/r/FireEmblemHeroes/comments/9hxwpt/rival_domains_auto_grind_cordelia_classic/