Contacted Tracertec, they came back almost immediately - they have an odd clause where you can only move the device between cars within the first two months - so I think that'd rule them out. I'm waiting for clarification.
CTrack haven't responded.
Just emailed Matrix.
Won't go with Tracker, they had lawyers after me when the insurance had a device fitted to my car and weren't paying. It took months to sort out, and the bloody lawyers wouldn't get the message, phoning me constantly, threatening to blacklist me, etc, etc.
Netstar next...