I gained what little I know about sonar growing up with a an old Navy man/fish biologist. All fish finders, aside from the newer side imaging units, basically operate the same regardless of the cost. The difference exist in the software and how it interprets the information. Fish finders do locate fish as it is a matter of target density. Sound waves pass through flesh and bone quite differently from other objects so, the better the software, the better the returns. I don't have a unit on my kayak, but I have two units on my other boat. I'll use those units when I'm on a lake for the first time and I want to find where the structure is. Once I "know" a body of water I turn them off. Long before the battles began between conservationist and the U.S. Navy over the use of sonar and whales, George (the biologist I mentioned) told me that sonar drives fish down and away from your boat. I've always remembered his advice and even noticed that my catch ratio improves when my units are off. If you don't think those units can be irritating to fish, try swimming under a boat when those transducers are pinging away. You'll be surprised at how much those pings are magnified in water.