every one of them has speed and max speed on them. no matter the price they are pretty much as equally accurate as long as they are mounted to where they get good view of the sky.. under the seat doesnt work well.. i just use it for max speed and i keep it in my back pocket or zip tied to the triple tree..

 

Yes, even the lower price units have speed on them - this is a basic GPS function (speed, distance, location)

The higher cost models +$125 have maps loaded on them
The next step up is color

For $125 you can get the garmin legend which has speed, average and max speed, distance, waypoint, track log, elevation, compass, basic US map, and can also download more maps.