Worth merging them?

Sitting on 30,000 feathers, I'm thinking of promoting my other Black Knight. I just don't like the idea of merging them since he's an incredibly limited unit unless he becomes another Tempest Trial reward if they release a Radiant Dawn banner. He doesn't seem to get much from a merge, just 1 extra point in Attack and HP.

I just need an honest opinion whether to just merge him, but if the vote for merging is high I will also go with giving him Vengeful Fighter from one of my two spare Winter Tharjas.