I've used this option once or twice - there was a point in my playthrough when I was actually out of bonus XP.
That point was long in the past, and has not repeated.
I also feel it's important to keep in mind that, in practice, this isn't a one-story-point option, it's a two-story-point option, since you then need to separately 'mentor' them.
My preferred suggestion: An officer promoted internally should be level one, count as mentored without a separate story point expenditure, and have a personality and starting skill of your choice. That would actually be worth the combination of 'rare opportunity' with 'which also costs a story point'.