Been thinking about getting either one of these, leaning more so towards the Wifish black box and streaming to a 10" tablet.

My boat a Roberts 21 which already has 2 fish finders in it (Garmin Fishfinder 120 & an Eagle Magna III).

Both their transducers are fixed to the inside of the hull (on the center line of the boat, above a small keel which the Roberts have running the length of the boat.) They work OK but are a bit old-school.

My question is about transducer placement. Would it also work mounted in the bottom of the hull?
Or if it has to be transom mounted where would I line it up to? because it is a displacement boat (cruising at 7 knots) if I were to put it in the traditional location of a planing boat it would be submerged, is this OK or should it still be skimming the water so to speak?

thanks