I think the main point he was getting at is that the yellow tangs will often attack anything that resembles a conspecific...especially if there is only two in a tank.
If you went with a more peaceful trigger, like a Niger or Sargassum Trigger, you would be fine. To tell you the truth...Harlequins may be on the more expensive side, but they are not demanding at all.
I think the key to success here is to make sure you add the fish in the proper order. The Harlequin should be one of the first because they are very shy and surprisingly passive...then, depending on the final decision with the other guys, add the more aggressive fish last.