As long as you haven't been caning the engine just prior to wanting to turn the engine off, then you don't need to have the engine continuing to run.The danger of turbo timers is that they may keep a fuel pump running after a collision, and pump fuel all over the place from a ruptured fuel line.
A bit of common sense to back off during the last kilometre or so of your trip will negate any requiremernt for a TT. The Shell Sierras, at Sandown, only ever did a slowish lap of the circuit after a race / practice, then would pull into the pits and switch off the engine.