I dunno, collection is a bit secondary to me, which is why I actually have discharged non-dupe but somewhat redundant units before in the past. Still, Flamel does appear to have a more reliable skill than Sera and can heal herself while tanking so I can see the argument for her being superior despite the potential cost difference. I suppose I could also just save some crystals by only using natural regeneration on Sera farming when her event hits and then just use her as a CC50 backup. All it costs me is a little patience anyway--I now have a Gellius to go with my Bernice so it's not like I desperately need the DK tank support.