Dysl3xiDogThey are very sensitive to unk and pen. When it works, they are really nice to write in imho. Tii bad most inks will easily bleed through. I don't experience much feathering, but I stick mostly to EF abf Fine nibs. Also, it helps that I prefer to always prefer inly writing on the right side of a book, almost never on the back of another written page. Very few books have no kind of see through in my experience.