While many new interfaces for musical expression have been presented in the past, methods to evaluate these interfaces are rare. This paper presents a method and a study comparing the potential for musical expression of different string-instrument based musical interfaces. Cues for musical expression are defined based on results of research in musical expression and on methods for musical education in instrumental pedagogy. Interfaces are evaluated according to how well they are estimated to allow players making use of their existing technique for the creation of expressive music. Keywords Musical Expression, electronic bowed string instrument, evaluation of musical input devices, audio signal driven sound synthesis