From what I can read it is a tweaked 705 with a touch screen. I own a 705 and like it. I bought it because I travel and I ride bikes; which means I have to navigate in areas with which I am unfamiliar. The 705's mapping function allows me to navigate with reference to physical locations while in the car or on the bike without having to find, purchase and use a paper map. Or, since I may be in several places on a trip, multiple maps.

If all I needed was the ability to navigate with reference to GPS points I'd save some money and buy the 500. If I were primarily riding in the same geographic area and didn't need to navigate I would buy neither. A good heart rate monitor and a cheap bike computer would do the job for a lot less money. Unless you are a racer, of course, is which case you are in a whole different world than me and cost effectiveness is no longer the issue.