https://www.youtube.com/watch?v=vRnX2cZOTks
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I don't know about the smaller units but I found the Humming Bird absolute trash on my kayak. Horribly, clunky interface, super power hungry unit and lost bottom continually in the ocean (50-150ft) (this wasn't a transducer issue either).
I'd highly recommend the Lowrance Elite 2 series 5" for kayaks.
The Lowrance Hooks used to be the go to for kayaks but they fairly recently changed their connectors on the Hook series to pressure fittings and they are terrible. I know quite a few people who have had failed units due to this.