[catnaroek]

Even ignoring real hardware, finger trees are only efficient in an amortized sense where more specialized purely functional data structures offer better real-time guarantees.

(0) Asymptotically optimal heaps: Worst-case O(1) insert, merge and findMin. Worst-case O(log n) delete.

(1) Asymptotically optimal search trees: Worst-case O(log n) lookup, insert, update, delete.

(2) Asymptotically optimal deques: Worst-case O(1) cons, head, tail, snoc, init, last.

etc.

Another downside is that they require somewhat fancy language features (namely, polymorphic recursion) to implement in a type-safe way.