I have one of these fitted in my car.
As you say its handy to warm the car up but i didnt like the handbrake idea as the handbrakes arnt that good in a 5 and you could probably drive away without releasing it.
I have been thinking about maybe trying to connect it up to the footbrake instead. Another bad thing is that it exposes all the ignition wiring to the back of the timer and could be easily tampered with.
Apart from that it is pretty handy to have.. I set the timer and jump out of the car and lock the garage because all my keys are on 1 keyring
