Used a fishhawk on Ontario. Worked....sometimes. There where times where the receiver didnt get the signal from the probe which was annoying. Helps to know temp but speed at the ball is way more important. All of these cold water species will move "out of temp" so to me the critical data is speed at the ball. Especially when fishing lakes with current. Aside from that, modern finders are so good at marking fish we never search for a prefered depth via water temp because we see where the fish are hanging. So in my humble opinion the only use for those expensive devices is to ensure an accurate presentation via controlling your percise speed at the ball. (We fished Ontario a bunch without one and that is particularly difficult.)
Jethro I think there is value, specifically if you troll a lot. If you divide the cost by how much you'll use it and consider how much money is spent on all other gear it seems like a reasonable investment.