I'm currently working on building an armor team with H!Henry, H!Jakob, and Arden. I also played around with using either my 4* Effie or Cordelia with Guidance Sacred Seal.
Having 1 Armor March is usually fine but feels pretty bad on maps where you start with your team split, so I've had better success with Cordelia.
My first H!Henry is +Res/-Def, who I already leveled and SI'ed. I also got a +HP/-Def H!Henry after that. I'm considering merging but then I lose access to my only second Armor March.
For the record, I also have 2 Hectors, and 2 Black Knights built up but have found them to synergize worse with this team since they have weaker player phases,
Merge would give you 1 point to res and 1 point to hp (I think) and the merge status would grant you one extra arena point. Since these two Henry's will most likely be your only ones, you can judge for yourself if it's worth it. I think that keeping one for armor march is a better idea.
Henry is easily the best armor unit there is, none of his skills are exclusive (Amelia is not limited and currently in a banner too) so I think keeping him is the better idea generally.
Though this is coming from someone who still has his spare Summer Gaius in case i want someone to use def ploy...
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