I have NASA brand depth sounders on my Flinders, centerboard on my Core Sound, and plan to use NASA brand on my (way unfinished) Looper 30. The display is large, seems to work well, not ridiculously expensive. On my Flinders it just “shoots “ through the hull so no hole, just bond a piece of PVC pile to the hull, plop the transducer in and fill it with baby oil, then glue the top on.