Like danimal said... HOLY *****!!!

I have the manual version - it is severe (putting it politely).
I've just installed the Sprintbooster this morning, and gone for a quick drive.
Once the car is moving it's fine - it's just trying to get the car moving without 'kangarooing'.
Fortunately these cars have traction control - without it you'd never get the car moving without chirping the tires.
It's going to take some accelerator/clutch synchronization before it's smooth.
It's a lot easier to set off in 2nd gear.
If anybody else is planning on getting one of these, I would think long and hard about the version for the automatics.
Having said that... I'm sure in a week, after I've replaced a set of rear tires, I'll say that the manual version is the only way to go!!!

Maybe I'll write an update in a week!