Not a terrible experience, just a... disenchanting one.
As much as the thing is hyped up, you'd think it has all the pizazz of a drinking a cocaine & viagra martini out of Halle Berry's navel.

The simple fact of the matter is that the sprint booster changes the WOT position, and that is all. Anything else is... well, I'll be nice and say "perceived."
If changing the WOT position is what you're after, more power to you. However, I think it's a horrible disservice to fellow XF owners to claim it does otherwise.

Remember, folks... you'll hear plenty of stories here about how the car "feels so much faster!" after simple things like K&N air filters or a cat-back exhaust - both of which, when installed independently, will give you negligible actual horsepower gains.

Once again...
FACT: The sprint booster changes the WOT position of the accelerator.
PERCEIVED: everything else that is said about it.