Hey
@F AJMI, I think that it is something that many law students do so it is not frowned upon, however it is overly used, and I feel like it will not allow you to distinguish from other candidates. This is my personal opinion of course.
I feel like it is fine to mention a subject you have studied, but I would not mention it as the only reason why you developed an interest into a specific practice area that the firm offers. I would stress how also other factors, such as a personal anecdote or an experience you had allowed you to see how useful that practice area can be in the future for many people/clients etc. This way, you will attract the attention of whoever is reading thousands of applications from law students who are probably mentioning that same module and you also have something to talk about during your interview if they were to ask you something around what you have said.
For example, when I was applying to
Gibson Dunn last year, I stressed the importance of the litigation department, which was what attracted me to the firm. Rather than linking this to an online course I had done around litigation and arbitration, which would have probably been easier to do for me, I linked it to an experience I had at an EU institution which exposed me to litigation procedures which I found fascinating at the time. This sparked the interest of graduate recruitment, which was very interested in hearing my experience. And it worked out perfectly for me!
I hope my suggestions are helpful and good luck with the application cycle!