In this work, for the first time, we present observations and data analysis concerning the usage of a commercially developed and clinically approved surgical navigation system, which incorporates monitor-based Mixed Reality (MR) visualization, during real-life surgeries. We analyze the usage of interchangeable Augmented and Virtual Reality (VR) visualization modes by the surgical team and report on our observations in over 100 Freehand SPECT acquisitions within different phases of 52 surgeries.