I have used the G-tech in other cars, but not in the X5. In any case they're easy to install in any car and once you get it calibrated they're pretty handy. For some vehicles it can be difficult or impossible to get the tachometer synched up (2 of 7 vehicles I have tried) but that's not fatal. Also, the bracket is cheap and mine broke on track, but I think I'm going to use the DL-1 next year anyway.
If you simply want to use it for 0-60 and 1/4 mile times you can probably go a little cheaper, and if you want a real track setup (I don't imagine you do for the X5) then you probably want to go to a GPS solution (which is now under $1000). Escort sells a cheap accelerometer unit for straight line acceleration for about $100, called GT1. I gave one to my brother and he liked it just fine. What do you want to use it for?
You should know that one problem with the accelerometer sensors in trucks is that a lot of pitch/squat under acceleration can throw off the readings. That said, still handy enough for what they are.
I found this article handy when I was shopping:
http://www.caranddriver.com/features...ters-work.html