I have the one that ESP sells, actually got two in like 2000 or something for $800 total.
Anyways, I primarily got mine for the dry starting of the motor and not really for the turbo but it's a nice feature and I let mine stay on for about 2 minutes after it shuts down. IF you can keep the motor and turbo alive it's worth it, if you rebuild or race a lot, not sure it's worth it.
This is not going to save your turbo as coking is not really an issue that comes up with our turbo's so I'm not sure I'd spend $500 + on this if that's your mine goal.