I HAD the 500, but switched to the 800.

I liked the 500, but two things soured it for me:

1. The display is smaller AND of a much lower quality than either the 705 or 800. No night mode (white numerals on black). A dingy bluish background. Clearly, the display is where Garmin skimped, compared to the other current and past series. To read the display required me to concentrate on it - focus in. The displays on the 705 and 800 can be read at a glance, even with six data displays on the screen.

2. The grade % / altimeter has a lot of lag (compared to the 705 or 800) and is sometimes wildly inaccurate. At times it would indicate a downward grade when I was on a steep climb and vice versa. Essentially worthless. On the 705 and 800, the grade % readout is quick and accurate. Very trustworthy.