We fish mostly in open water where the bottom is 50ft+, I thought the other transducers might give a wider coverage area. After searching around some, I've read that the "DI" units cannot use any other transducers, I've not seen a lot of benefit to the DI in our application, so a stronger 2D signal sounds good. I don't know how shallow your shallow water reference is, but we're not in less than 20' very often.