800s are fine, but you need to know how the firmware breaks.
- longer thans 24 hrs recording will lose all your activity
- Auto power off on a paused but not finished activity will wipe it (turn off auto power off in settings)
- Multi day events, if you don't backup your recorded rides, once it runs out of space it'll delete the first one, etc etc. I lost day one of TD this way (was saving to internal memory)
I split my routes into 200 mile segments for Tour Divide, didn't use turn by turn, but did use cuepoints for some turnings and also city limits of major towns so I could see in the cue sheet how far the next town was from my current location. Very useful in the middle of the desert to know that it's 83 miles to the next town, so you can ration water accordingly.