The Fifth Head of Cerberus is three novellas Frankenstein-ed together, it lacks the cohesiveness that Wolfe’s Book of the New Sun has. It feels like a prototype of what Gene Wolfe would go on to write.
Unless you’re a super fan of Wolfe’s work, I don’t think these novellas are worth reading. Even if you are a fan of his work, some parts of these novellas will be torture to read. Definitely not my cup of tea.