I’ve fitted them to our fleet of vehicles along with several major items of plant. We don’t really use them to keep tabs on staff, they’re fitted more from a security/deterrent perspective.
We only scratch the surface with the available info they give, as you mention speed, location, journeys made etc. We don’t pay staff using the tracker data but if we suspect they are taking the proverbial we will cross check the tracker data against time sheets.
Our units have an internal backup battery which will last for approximately seven days if the vehicle battery etc is disconnected. I will also receive an email if the battery/gps aerial is disconnected which will give vehicle details/location etc, any plant that is towed away out of hours will also send me an instant email to say it has been towed away.
I also have an app on my phone which give real time mapping/speed/journeys made etc. Really clever stuff which can help save money along with assisting servicing schedules etc.