They are good for the money. You have to set it up and turn features on and off by sending the unit a text message which is easy enough, and the unit will reply back confirming that that perticllar setting has been set. The problem is the are loads of features so it's hard to remember all the codes. There are apps available like the Back2you app, so for example if you wanted to arm the system you just press arm and it will automatically generate a text with the correct command and password for the device for you to send. It has 3 programmed buttons, Arm, Disarm and Locate Tracker, with only two extra that you can programe with what ever you like. Someone could be on to a winner if they could design a decent app.
I have mine set to send a text for the following
The toad alarm goes into alarm state
The ignition is turned on
The car battery is running low
The shock sensor has been triggered
The battery has been disconnected
It leaves the area that the car is parked in when armed
You can also set it up to alert you if the car goes over a pre defined mph, handy if you're leaving your car at a garage
It has a built in mic, so you can ring the tracker and listen in to what's going on in the car
It's also linked to the back2you server and for £10 a year you can have live tracking which also stores all the data
HTH