Transom-mount transducer vs. through-hull transducer?

[Mike in SC]

I would like to know how this ended up, and what Cobalt does with factory installation of the transducers. They're probably not interested in the fine detail you can resolve with the latest fish finders, only raw depth info.
I would personally like to map out some known shallow areas and rocks in our lake and mark them as hazards...not sure a glued in transducer will do that.