I have kind of a Nino-centric team which is obviously led by a 5☆ Nino. I also recently obtained another Nino, but this time, she is a 4☆.
I have been trying to decide whether I should unlock the 4☆ Nino's potential for the sole purpose of merging with my existing 5☆ Nino or if I should just save the feathers to unlock another hero's potential later on, for instance, the heroes that are obtained through Grand Hero Battles as 3☆ or 4☆ only.
What I want to know is whether the benefit of having a level 40+1 5☆ Nino outweighs the benefit of unlocking the potential of a 4☆ hero into a 5☆ one. In general, is promoting for the sole purpose of merging worthwhile or cost-effective, or is it best to only merge heroes if I happen to get two of the same 5☆ hero?
For context, I have been managing to get quite a bit of feathers per Arena season (5k+). Combined with regular missions, I think I'm making roughly 7k feathers per month.
UPDATE - Just to give a little update on how my experience went
I did promote some heroes to 5*, but ended up sticking with my original Nino-centric team. Putting up a new solid team together is pretty hard, and I decided to focus on my main team while I don't have enought 5* heroes to make another arena competitive team.
I found that promoting the Askr trio was the most benefical choice to do with the feathers, and after that I went for the Super Nino, which is now +7, truly a powerhouse.