Depends on your boat---what is it?
Number one thing is the two Side Imaging pulses "see" right and left from the water's surface to past vertical under the transducer on both sides. If you want the best Side Imaging you have to attach the transducer to the hull so it can do that.
Number two is if you want the transducer to give you depth when on plane, the bottom of the transducer has to be slightly below the bottom of the hull so it has water contact when on plane.
Some that have just one SI model will position the display so it can be seen from the bow and at the console. A swivel mount will do that.
Some will install a transom transducer and power cord at the console and the same at the bow, then move the display to their position on the boat. That is what I did with my first SI unit.
Next is image quality. The unit comes with the Compact SI transducer that is 4" long. You can use the HDSI transducer that is 6" long to get sharper images. That is because the longer transducer produces a thinner SI pulse.