If you look at the offerings from Lowrance for Hook2 7" models you will see many of the same features spread over quite a price range. Some model might cost $600 and have Chirp 2D and DI and SI. Another cost $399 and has the same features, minus mapping of some sort. My question is about the quality of DI and SI in a lower priced model as opposed to the same features in the higher priced model. Are they the same, or have corners been cut? I am not the least bit interested in mapping, but I do appreciate GPS that allows me to see the speed at which I am getting hopelessly lost !!! ;-)