Follow-up question: do you promote 3* for your 4* merge projects?

Attempting to get a 4* of a specific unit can be a pain and costly. 2000 feathers isn't too much to sacrifice. That unit could also have good IVs that you may want, so to me, absolutely.

If you've been saving up for a merge project, odds are you already have enough to merge, but what happens when you find a new unit that you want to merge? Probably won't have the units to merge up. You take what you can get.

2000 feathers is chump change - You get 3000 every week just for one run in Arena, so absolutely! I've been waiting on my #11 Catria for over a year now (+Res -HP pls), but I have 15 books of Effie (+2 in Barracks) and 14 Oboro (+2 in Barracks) to show for it...

I dunno why but usually 3* copy has superiour iv than 4* for me in most cases, so it is worth it. Let me give you example of my A!Tiki, who is 5*+8 at the moment, majority of promoted copies of her was 3* at base, one of those was free 3* A!Tiki from three heroes quest.

If it's a unit I really want to be good, I will promote them but if it's a unit who I'm merging just in the hope of them getting a prf weapon, I'll save the feathers for 5* merges.

Yeah, I have totally done that multiple times. I'd rather spend 2k feathers, which I can make back really quickly, than wait for months for a 4* copy.