The metrological performances of a SPR-based sensor exploiting the plasmon-triggered switch effect are investigated in this article. The switch effect, recently demonstrated, is a lossless energy transfer phenomenon between the 0th and -1st diffracted orders, through SPR excited modes, which only occurs in a deep metallic grating while the incidence angle or the wavelength varies. A differential measurement of diffraction efficiencies of these two propagative diffracted orders and an optimized signal filtering, allows to retrieve the sensing signal at a fixed wavelength or fixed incidence angle. For a deep metallic grating illuminated under TM polarization, such a sensor provides a high sensitivity and a limit of detection lower than 10-7 RIU reaching thus the limits of the best current plasmonic methods. The theoretical sensitivity and measurement uncertainties are rigorously investigated considering digital signal processing in order to provide an optimized signal processing and thus increase the sensitivity and the current Limit of Detection (LOD). Due to its performances and its implementation simplicity, this new SPR based sensor is very promising for the detection and quantification of chemical and biological species both in liquid and gaseous environments.