If he did decide at some point to buy a subscription, the simplest way to enable it is to send a signal to the sleeping-but-live tracker. Else he'd have to go to a dealer for some "factory authorized" service. That might not be reasonably done in some locations.
Giving up privacy in exchange for convenience. This should be an opt in feature, not a company tracking your every move and doing who knows what with your data. Even when you don’t pay for said feature.
There could be a physical switch on it that keeps it turned off. The owner could then turn it on when they want to activate it.