Returning to explore the details of the Oculus Sonar, the M750d and M1200d offered by VideoRay are both Dual Frequency sonars. Only one frequency is active at a time and the control software interface allows you to select which frequency to use. This information will help you make that selection.
Navigation mode uses the sonars' lower frequency (750 kHz and 1.2 MHZ respectively for each model) and is characterized by a longer range due to less attenuation, lower resolution based on the lower frequency and a wider field of view due to the individual beams having larger angular spread and therefore requiring more angular separation between each beam.
Identification mode uses higher frequencies (1.2 kHz and 2.1 MHz respectively) and is characterized by a shorter range due to more attenuation, but a higher resolution. The field of view is narrower because the angular spread of each beam is less and the beams require less separation.
The modes are aptly named. When searching for objects or for general navigation, Navigation mode is preferred. Once a target it observed, switching to Identification mode will provide more details to help identify what the object is as long as you can get close enough to be in range.