The definition of smart devices for semi-active structural control is well represented by semi-active magnetorheological (SA MR) dampers. SA MR dampers can be used as reactive force generators, when the control algorithms adopted to drive the devices are derived in the framework of the control theory, or as smart dampers, when the real-time change of their mechanical properties has the aim to provide, at any time, the optimal amount of damping in a structure. The two approaches have different requirements in modelling the SA MR devices. On the base of the results of an experimental campaign on 2 prototype devices manufactured in Europe, the present paper compares the effectiveness of numerical models presented in the literature and analyzes their response time and dissipative capability.