The problem with GPS devices is they are designed to do one thing and one thing only, Windows CE can be customized for whatever reason the vendor wants, so all the parts of Windows CE which are not needed to do this one thing are left out, which is fine if the device is to be used as intended, Problems arise when it is not, The Mio/Navman devices with the three position switch do not handle a suspend request properly, most of the time switching straight back on again.
Here is a little script i wrote a while ago that will suspend the device on loss of external power.
The scripts you linked to above use the notification queue to run the ScreenOff/On utilities, These just turn off the screen so the device is still on, however on some devices it just turns off the backlight. And they don't work on every device.