Hi,
SOP aka Statement of Purpose is always a better idea to write, this will give the VO insight of your intentions.
Duration of course is not what matters, important is you express the VO, how this course will help you, what advantages you will have after doing this course back in your home country, statements which gives indication about the importance of the course at the same time hint that you will surely return back after course completion as this course will give you added value in stream of job.