I have had several cheap ones and for a kayak the Eagle 168 and the next one up are all you need. The tem guage even does well thru the bottom of the kayak.
I had two of the old Piranas that only read in feet and not 1/10's like the eagles and they did not do as well. Also had one break even though I used Corrosion x on the cable plugins. P3 had two plugs instead of just one on the eagle.