I have a Dual beam 20/60 on my trolling motor. Thanking about adding a Quadra beam 20/60/90 degree transducer to the tramsom. With the 90 deg. beam would have coverage of 2X THE DEPTH. Have any of you used the quadra beam and what did you think of it. Would cost about $170.00 for transducer and switch. Or spend $300 to $490 for Down Imaging unit? The side image is out of my price range.