They work. They tell you speed and temp at the cannonball which is great if you can digest and use the information it provides. They are another source of information that can be very helpful or very confusing but you have to learn how to use them effectively and to do so you need to be on the water quite a bit. I run one and have learned a lot from it but now I only get out a few times a year, I'd probably be better off leaving it home. Just like a $3000 downscan/sidescan fishfinder, it's a great tool but it will not put fish in the boat by itself.