Battle forge is expensive for Druid, and mana flowers stick out of the corner.
Battle forge is against the spellbook style, which is spawn, spawn, and spawn some more.
Harmonize is cheaper both ways and compacts well.
your trees are just a too valuable target if they are harmonized.
if you also talk about battle forge expensive, the two harmonize already cost you two spellbook points more as the mana flowers do, so neither argument.
I get the thematic pov about battle forge though. I don't think both trees are good together (competetive), but if you go for both consider some back up. You won't have that much mana early on, and if you loose your harmonized treebonded tree you loose 3mana total a turn, thats extreme. With a flower it is less risky.
I would also think about the leaf ring. if you cast it first round you get two mana till the third round (like your first harmonize) and have channeld 1mana less total if you harmonized both. But you saved 6mana on the cast, giving you more oportunities. You save 1 action. If you then cast a mana flower on turn three you are on 1channel total less for future rounds but saved 1mana prior. Your tree's don't have that big "Hit me target" on them. And you save 2 spellbook points. optional you can use one more action if you have to cast another flower turn 4 (not sure if you need that much channel). The big bonus of this approach is one less action on turn 2 used and if you get under pressure you don't have to do the flower or could use some enchantment...
You also talk about fellela and butterfly? How do you play your games in your local meta? how long, cause this sounds like extremly long play builds and many situational cards in book
