I'm generally not a fan of them, but there are a few I don't mind--JJ for a girl (or sort of for a boy), EJ for a boy, KJ for a girl, MJ for a boy... that's about it, I suppose. I think my love for JJ stems from Criminal Minds, though, lol. And maybe JJ Abrams. I'm about 99% sure there's not a show he's developed that I haven't loved... lol.

But still, I would use the full name (or a common nn for the name) more often than the initials nn. Unless I purposely used the initials to come up with a nn I love, like Ella Violet, nn Evie, or Grace Gabriella, nn Gigi, or Monet Evangeline, nn Emmy. etc. The whole _J has always seemed like a wasted opportunity for a perfectly wonderful FN, to me.