Indeed I have, there usefulness (as fishfinders) is limited to the depth of water your fishing in but as feature finders they come into their own.firstly you should understand how they work, In brief! a conical signal is emitted, the deeper the water the wider the cone.sooner or later the signal will hit the bottom and bounce back,at this point what you will actually seeing is a change in density. you should be able to determine the composisition of the bottom a dark/black line will tell you that the botom is hard, probably gravel, or a grey band that'll tell you that the bottom is soft, silt etc.
You'll also be able to determine the terrain, holes and bars. It goes without saying you'll get a return from any thing more or less dense than the water that surrounds it. most things in the water are inamanimate so they give a solid return in varying degrees a fish on the other hand fortunatly for us! has a swim bladder and it is this that gives the fish away. Either you or the fish finder depending on the mode set can tell that a black shape with a light centre is a fish, of course there are things in the water that can mask a fishes presance like oxygen rich weed or a shoal of roach but with practice even this shouldn't be an obstical.
The size of a fish is hard to determine this is due to the nature of the cone, a small fish that travels through the centre of the cone will give a better return than a lunker the has just clipped the edge of the cone, all you will know is the a fish entered the cone and exited. Further more because your looking at a 2d screen of a 3d world and looking across a plan view you won't be able to tell the the direction of the fish or which side or end of the boat the fish is. Its hard to explain but with a bit of thought you'll understand. Another drawback is that an object has to move through the cone or you have to move over it otherwise a straight line will displayed on the screen.
In my opinion unless your fishing in a large and deep body of water your wasting your money. you will have just as good understanding of he water below and arouund you by using a lure with a braid mainline and for every minute your bait/lure is in the water your a minute closer to catching that big one you dream of.
Hope this helps,
Steve
