My co-worker told me about sprint booster when he was complaining about his Audi A6 being sluggish and wanted to try it. He bought it for almost $300 and was very happy with it.
I was looking around on Ebay and found one last week, used with no reserve... long story short i won it for $14 haha

My Co-worker was pissed!!
Even though it was for a 3 series it bolted right up, the guy from sprint said all the BMW's were the same, not sure why they have different part numbers but anywho..
I gotta say, this thing makes a big difference on how the X5 drives. No more sluggish pickup, you have the power available right away. I turned if off and on bunch of times to make sure i was feeling a difference and oh man, im stoked! You can have it off, one press gets you to green which is still a good improvement, second touch is red which is all out. I'll be keeping it in red.
The highway driving is sooo much better now, overtaking cars is a breeze. I will recommend this for sure. The fact that i got it for $14 is even better