I do know everyone that I have seen with the portable units havent been very satistfied with them, especially in the river. The only think you can really depend on is the water depth(when it reads), and they prove to be more hassle than they are worth, and spend more time sittin in their vehicals(or at home), only to be brought out when someone ask about them in a conversation, etc.
For in the boat, anything that is not mounted stationary is more of a hassle than anything. A hassle, is usually put in the corner somewhere out of the way and not used. I like to fish, not play wih toys. If I want to play with a toy, It will be a underwater camera.
A depth finder, no matter how cheap or expensive has to serve its purpose… To accurately show the depth, show structures, and show fish.. not false readings. Thats why I recommended the eagle cuda 168. Its cheap(around $70 if you search around), the has grey line(determines bottom hardness), and do a good job of showing fish… not some of he cheap units that will show fish inthe parking lot when you power them up. They dont have the super high resolution of the high dollr units, but they have a decent, accurate picture and a large enough screen to let you know whats going on. I believe they also have water temp.
Casting from shore, its easy to cast out a weight or jig and *count it down*. You can get a good feel for any area.
I guess what I am saying.. your better off paying for something you can depend on, and give you an advantage while fishing, and is not a hassle vs something that takes effort away from your fishing.
Maybe it would be an interesting *toy* to have, but I would own a depth finder before ever having an extra toy laying around.
Another option for a graph is the Bottom line fishing buddy’s that kind of look like a trolling motor without a loer unit. They camp onto the transom and show bottom, ad also have side finders(for what they are worth). These used to work very well on a Zodiak raft.. cat get much more portable.