I haven't heard of anybody using the Garmin Edge for testing but i have found it very useful for clutching testing.
After your test runs you down load the GPS to a computer and it will graph your runs.
Often i would bring a laptop to where i was testing and compare clutch setups in the field.
Its great because the only variables are the changes you do to the sled between test runs, you don't have to wait for someone else with a similar sled to test with.
I would do at least three test runs per setup, and then do a change and test again.
Consistant starts are very important, if i lost traction or hit a rut and had to back off i would abort and restart.
I found the speedo readings are about 8mph faster than what the GPS says.
It would also work well for testing engine mods etc.
Here are some sample graphs.Click to view attachment

Do you think those results are reliable enough for testing? Most GPS' have an update rate of 1/second. I've found with the two GPS' I have that they take more like 2 to 3 seconds to update speed. Your speed can change allot in 1 second when accelerating. What Edge do you have?

Up to about 50mph doesn't mean anything but after that the readings have been quite reliable. I always do at least three runs per test and they usually are very close, there has to be at least two runs that are almost identical and i use that data. Some times you get a curve thats shows to much speed,that doesn't repeat though. Bottom line is that if the sled is faster the graph will show it.
To compare curves against each other you have to shut the GPS off at the same time interval [say 20 sec.]
I have a 205 Edge.
I got well over a hundred runs logged on it, and it's like any tool, you have get used to using it and interpreting the data. I would not test with out it.
It's not perfect, i wish it had a higher update rate for more accurate low speed info. and more detail in the graph but it's designed for longer duration use, i haven't found anything better to use yet.

looks like that crossfire is a pooch!!! or the driver weighs 200 pounds more

The Cross Fire performed like any other one, the speedo reads about 8 mph more than the GPS readings i was getting, so it was getting about 100mph on the speedo at 2500' on a packed snow trail at about -10c, not the fastest conditions. not to bad. I did get 115 mph on the speedo with the same sled on icy conditions but that was a rare condition, the graph posted was more typical.
The point of the post was to show how the Garmin Edge can be used for testing purposes, the same sled run in different locations, altitude, and snow conditions [slow/fast] will have different results.

That is pretty cool! Thanks for shareing the info.

Does that GPS unit work pretty well for riding trails and uploading trail maps as well?