We can only make a technical recommendation against operational requirements. It's not proper just to examine the technology, itself. There is a range of issues, such as what is the interrogation interval for the device. Do you need to know where the individuals are every two hours, every three hours, or every five minutes? Where does the device have to work? What does it have to be able to withstand in terms of punishment or environmental conditions? We need to clearly understand that first.
On February 14th, 2012. See this statement in context.