Looks like Humminbird has added some new, low cost SI sonars since I last visited this topic. I'm looking to create some bottom maps using SonarTRX and Reefmaster. Just looking at the specs of the 3 sonars, their SI / DI capabilities look identical, the only difference (for my application at least) is screen size, resolution and networking capability. Neither software supports real time data input (too bad Dr Depth is no longer available) so I'm guessing the 398ci SI will do me. Or did I miss something?