Tangible user interfaces (TUIs) exhibit innovative interaction paradigms, for example through motion sensing, tactile feedback, or gesturing. Whilst wide spread in human-computer interaction, their value in robotic systems has still to be assessed. In this paper, we present some results obtained through an extensive experimental evaluation of motion sensing interaction paradigms implemented on TUIs for the teleoperation of ground robots. Once analyzed the collected data, in order to evince relevant properties of TUIs, we provide a detailed discussion of our results in terms of mission-related performance, environment conditions, robot operation degree, and human cognitive effort. Our belief is that such a study represents a valuable step towards a formal assessment of tangible interfaces in robotics.