I have one. It's great! You can really substantially increase your milage if you want too. The trip gages are really nice. Once you plug it in, it automatically turns on and off with the engine.
I have it mounted with velcro low on the dash near the door. Not ideal location when entering the truck. I used an L shaped piece of aluminum, that wedges between the lower kick panel and the dash. So it is supported by the bracket and velcro. No screws to hold it on. the cable hidden and runs only a short distance to the diagnostic plug which is right under the steering column.
On my 2002 XLT, it has a compatibliity problem which causes it to crash ocassionally. When it does, the display goes blank and the trip data gets messed up. I figured out how to set the default settings so it will reboot as soon as it crashes. Before that it was a pain to remove and reconnect the cable while driving. Even with this bug, I'm happy with it.