I know I'm speaking for myself, but to me the most important characteristic is that I am forced to estimate/calculate the displacement/tonnage/dimensions of the ship, like real Kaleuns did. The addition of many new merchat units is great in that it forces you to stop browsing the ID book in the hope of getting an exact match (There were hundreds if not thousands of merchant ship models around in WW2) and have the risk of a bad estimate and wrong firing solution.
Looking at both merchants you depicted, I would make the following rough guess as Kaleun for my target data:
-Tanker, split superstructure
-Approx 6000-7500 GRT
-Aprox 100 metres long (For a fixed wire speed measurement)
-Aprox mast heigth of 22 metres
And that's one of the nicest part of the game for me, which your mod improves considerably