I currently have 12 WC mellleri. They are all healthy and social with each other as well as people. We also have 2 oustalets - one is WC.
I have found that where you get them matters. Some people/places care for them better prior to selling them while others do very little to ensure long term sucess, just wanting a quick turnaround on them.
That said, I've only lost 1 recent import melleri and 1 recent import oustalets (she was eggbound and emaciated when I got her.) I lost 3 other LTC melleri that I acquired in very poor condition (infections/emaciated/dehydrated) due to poor care by the owners. While I hate losing any, I did learn a lot from them that has helped me care for other "rescues."
My goal is to breed the colony I have and work with other melleri keepers/breeders to establish a sustainable CB group. Unfortunately, many people seem to not stay with melleri long term and they are rather slow to breed ...