Your first point is fair. Of course, 'readability' is extremely subjective. It should always be judged in terms of the intended audience for the code - we'd have to ask a Haskell programmer to be sure.

Your second point I disagree with completely. Duff's device is non-idiomatic C that relies on oddities of C syntax (fall-through of cases in a switch statement, and the ability to jump into the middle of a loop). My code is reasonably idiomatic Haskell.