Thanks to the seller my devices were unlocked which means I'm in control of who the tracker reports location to and I choose the SIM card. Nice one.
Once you've tracked down the correct configurator for these Teltonika devices (this one needs the Telematics Configuration Tool) , they are very easy to configure on a PC over Bluetooth and have many more options over and above a simpler tracker.
The tracking is excellent (Satellite choices include GPS, GLONASS, Galileo and BeiDou), and is sensitive enough to report position even in some multi-story car parks if you're nearer the roof. Because you can select more than one Satellite type for the location calculations, even urban canyons track very well.
The bonus for my needs though is the reporting of the car's battery voltage.
Most cheap trackers only report their internal battery voltage, but if it's fitted in a car and that starts dropping below 4volts it's possibly too late to save the car battery from over discharge damage.
This tracker reports the supply battery voltage, and can also report voltage of another battery too, and as I have two batteries in my car they can be monitored & reported separately.
Lovely little unit.