The difference is that tlhIngan Hol was created to be spoken in movies and shows, not just to explore the parts of language development that were interesting to the creator. So <i>usually</i>, the tlhIngan Hol used in Star Trek movies and shows is about as good as it's going to get. Sometimes the actors have terrible pronunciation, and sometimes the writers make up names for people and places that aren't actually possible in tlhIngan Hol phonology and we have to just roll with it. And modern Star Trek shows have mostly done a better job than the classics, because they bother to have a Klingon language consultant on staff (I was gobsmacked when in ST: Starfleet Academy they used "qeylIS" and "Qo'noS" rather than "Kahless" and "Chronos") . But unlike Quenya or Sindarin, you can have an actual natural conversation in Klingon, as long as you avoid topics for which the Klingon Language Institute hasn't developed vocabulary.