28 to 30 is the big jump; 30 uses a different transducer and therefor can do different things the others can’t, better things. 28 uses the same transducer as the 8 and 18, just the display that’s different. I assume the 38 is basically the 30 with adjustable zoom
28 doesn’t have the same ducer as the 8 and 18. 28 has the pro-view ducer