Fish finders for float tubes

[AbFlyFish]

Hello,

I have been thinking about purchasing a portable fish finder for my float tube. This will be used to fish for trout in freshwater lakes in Alberta, Canada. I am leaning towards the Humminbird PirahnaMax10 or the Eagle Cuda168. Does anyone use these? Thoughts?

Also, I am a little unclear as to how the transducers work. Does the transducer look below you only? When they talk 20° or 60°, what does that mean?

Thanks.