The "X" in Elite 5X means it does not have GPS. You might also find that it does not come with a transducer (if it says "head only" or "no transducer") and that's another $80-$100

HDI means "Hybrid Dual Image" ... which is regular color 2d broadband sonar, plus Down Image sonar. 2d sonar puts out a cone shaped ping & registers on the screen as colored patches/blobs to represent what's being "seen" within the confines of that cone shaped signal. Down Image puts out a "fan shaped" (wide/thin) sonar ping & registers on the screen as a picture-like image of what was just passed over.

Humminbird & Lowrance both have good units in that price range. But, first .... we need to know what you expect/want the unit to do for you, where you're going to mount the transducer & head unit, and what style or fishing methods are you going to be using. If you need to know your speed ... you're going to have to go with a unit that has GPS capabilities.

... cp