Is it also intentional that Sanguine Signet does not seem to work with Fern? And Reeler? (Reeler makes sense but I'm not so sure about Fern...)
I've tested it on Fern, and it does work, though Fern's healing mechanics can definitely be confusing. Fern gets 50% extra healing from restore cells, so instead of the usual +20 stamina per restore, she gets +30. For overheal, restore cells only heal for half the amount (rounded down). So if Fern is at full stamina and collects a restore cell, she'd receive half of that healing instead.
Oh, that would explain why it is difficult to keep track of how much is getting healed with the Sanguine Signet! I don't think I had internalised the overall complexity! Apologies!)
Gotta admit that Fern is my favourite even though I'm not sure if some of the others aren't more efficient for others jobs or even overall! :)