I have had a BassLink (not the BassLink II) in another car (not the X5) since about 2000, and I love it. It still works flawlessly.

It doesn't take up a lot of space, yet the low end is impressive for such a small unit. Installation was fairly simple.

It is definitely not powerful enough to make the cars around you shake, but I felt that it was more than powerful enough for inside the car.

If you go for it, the only suggestion I have is that you should try it in a few different locations and see how it sounds before permanently attaching it to the floor.