@Akira: First thing, don't buy that piece of crap ICD are overcharging for. Perhaps buy from
Power, for less money and a better model.
As for fitting: in a tower, the port sits in a backplane. Desktop A1200 - just run the lead from the unit out through the back of the case and connect the port to the monitor. No need for 23 to 15 pin adaptor.
If you don't like the idea of a lead running out of the A1200 case, maybe an external unit would be a better buy. It depends on whether you ever intend to buy a tower case. Once an internal unit is installed it is invisible: its output port simply replaces the existing Amiga ones. Nothing protruding from the back of the Amiga, as would be the case with an external model.
Your choice, dude!