I'm no expert by any means, but I've done a little bit of reading on it. I think all cheap FF/GPS' do all the things you really need them to do, its just the presentation/resolution/color and all the extra features you have to make a decision on whether you really need them or not. I tend to overbuy with tech stuff, but on a kayak I just need to know that I'm on the spot, how deep it is, how deep the fish are in the water column, and maybe how high the reef or structure extends off the bottom.
Thinking a little deeper into it....
- Its has to be easy to use on the yak and not too big that its heavy or in the way.
- Has to have enough memory capacity for a few hundred waypoints. I'm pretty sure most do.
- I need a dual beam model because I fish the sound pretty often which is mostly all shallow water...(1-20 feet), but I also like to get out in the gulf.
- Color is nice to have, but not a necessity for me.
- Being able to distinguish between larger fish and smaller fish is a nice to have feature for me because I'm likely going to fish the spot anyway if I paddled out to it. Distinguishing bait from other fish however is important.
- A map feature is nice to see where your other marks are in relation to your current location. I don't care too much about chart plotting views, but a map showing multiple marks will help you make decisions on the water. I think most do this anyway.
- The extra map modules they sell you can be really expensive and some aren't all that good. That seems important to know if you travel a lot with your yak.