In the framework of the Horizon 2020 project C3HARME, an experimental campaign has been carried out to characterize a new class of Ultra-High-Temperature Ceramic Matrix Composites (UHTCMC) for near-zero erosion rocket nozzles. A novel test set-up has been developed to the purpose of testing small-sized specimens, with ZrB2- based matrix and carbon fibers, exposing them to the supersonic exhaust plume of a 200N-class hybrid rocket nozzle, employing gaseous oxygen as oxidizer and High-Density PolyEthylene as fuel. The aim of the tests was to reproduce realistic rocket nozzles operating conditions, in order to demonstrate the ability of the specimens to preserve their functional integrity in a relevant environment. After that, a UHTCMC nozzle throat insert has been manufactured and experimentally tested to verify the erosion resistance and evaluate the effects on the rocket performance by comparison with those obtained in similar operating conditions employing a graphite nozzle. Computational Fluid Dynamics simulations supported the experimental activities allowing for the rebuilding of the thermo-fluid-dynamic and chemical flow field and the characterization of the test conditions.