Humminbird transducer: transom mount vs. inside

I just recently purchased a Humminbird 565 fishfinder. It comes standard with a transom mount transducer. This model fishfinder has a dual-beam sonar, 20 degree cone and 60 degree cone. I would like to mount the transducer inside the hull, and Humminbird offers a transducer exchange program so I can exchange the transom mount transducer for a puck transducer that is designed for mounting inside the hull of a fiberglass boat. However, the puck transducer only appears to be a single-beam (20 degree) transducer. I called Humminbird tech support to clarify, and the person I talked to said that I would not lose any capabilities of my unit. I will call back again tomorrow to get a more clear and defintive answer.

So I have two questions for anyone who might have experience with this: 1) Do I have to give up the dual-beam capabilities of my fishfinder by mounting the transducer inside the hull? 2) What are the drawbacks of mounting the transom mount transducer inside the hull of my boat, instead of trading it for a new puck transducer?

Thanks very much.