Ellipsometry and Multi-Parametric Surface Plasmon Resonance (MP-SPR) can both determine thickness OR refractive index.
Spectroscopic ellipsometry (SE) and MP-SPR can both determine thickness AND refractive index.
The main difference comes from the samples that the techniques can work with, which is given by the optical set-up of the two.
The difference in optical set-up of Multi-Parametric Surface Plasmon Resonance and Ellipsometry.