When I had a U-boat II I bought a Fishing Buddy 2250 and it worked pretty well, and was good for both fishing out of the tube and ice-fishing, though the 9-degree cone limited what you could see in shallow water.* I transferred it over to my FishCat 8 pontoon and made a custom mount (no more straps) and it allowed me to find some neat structure and schools of suspended fish.* The one problem was that the custom mount vibrated whenever I was moving at trolling speed and I couldn't get an accurate reading.
So, after a couple of years I asked for a Cuda 250 S/Map combo sonar and GPS.* I installed it this summer and made a custom-swinging mount for the transducer.
Here's the Sonar/GPS unit installed.
Here's the transducer mounting.
I decided not to use the stock battery (it weighed about 5 pounds) and instead got a smaller 2 AH 12V that works just fine for the trips I take.* The sonar works great, even at trolling speed, and with the wider cone angle I can see more fish in shallow water.
Now, if I don't want to take the finder with me, I just unclip it from the mount and swing the transducer up out of the way.* The sonar is also portable, so I can use it on the ice.* If I do want to use the sonar on the pontoon, I just snap it into place, drop the transducer, and we're in business.* Having the GPS is nice too...now I can mark those "interesting" spots when I find them, instead of scribbling down visual bearings and cross-references.