This contribution presents the assessment, on both the maximum electron density (NmF2) and the corresponding peak height of the F2 layer (hmF2), of the overall performance of such ionospheric key parameters inferred from Radio Occultation (RO) measurements for a period of more than half a solar cycle between 2006 and 2014. One of the satellite constellations allowing the retrieval of RO measurements is the FORMOSAT-3/COSMIC mission. It collects occultation measurements since 2006 and has been exploited for establishing a database of RO data between June 10th, 2006 and April 29th, 2014 for this study. Such data set is compared to ionosonde measurements provided by the global Space Physics Interactive Data Resource (SPIDR) network in order to infer information about the reliability of retrieved F2 peak parameters during different solar conditions. Emphasis will be made on how important the outlier detection process becomes in the analysis of the RO-derived data and comparisons will be made between results obtained using a rough and a tougher outlier threshold rejection while carefully filtering the SPIDR ionosonde data for the inter-comparisons. The key aspect of this study is to highlight the importance of the screening processes of the reference data used to validate the obtained results. This process is crucial since it can totally bias the results and mask the effectiveness of the RO technique. Such results will evidence the necessity to properly filter the reference data that has not been manually calibrated. Climatological investigations as well as comparisons between the radio occultation and ionosonde F2 peaks are carried out based on the ionosonde reference data under varying conditions. The presented work can be of high interest for both, the radio occultation and the ionosonde community, since the impact of the pre-processing and data screening of the ionosonde data is also addressed in this study. In this way it is provided a most clean and realistic view of the important contribution of RO technique to ionospheric sounding.