I got by just fine with my Hook2-5 on my kayak, and even had it on my new 17' boat a few weeks while I decided what to buy. It has DI, 2D sonar, and the mapping with a Navionics+ card that came with it is completely adequate for the lakes I fish. The cheaper models have less adjustments and settings than the full-featured MFDs, and rely on auto settings a lot. Probably have less power and transducer choices as well. I know I caught a lot more fish after I got it than I did without it.
"Alive without breath, as cold as death; never thirsty, ever drinking, all in mail never clinking."