I know it's an old thread, but the LATCHes really need a workout before they become much easier to use. More specifically, the leather around it. I do my carseats a little more than I would like but now it's like a 30 second job to put one in and lock the seat belt through the hole in the back. On a loaner 3-series I couldn't LATCH at all despite trying to dig the leather up and push the carseat's latch buckle in the same way on the X5. Design issue on the LATCH anchors.
As for the seat-backs... BMW designers did a good thing here by not making that full leather. The hard plastic is very welcome - easy to clean and doesn't have scuffs from plain old kid shoes/sneakers. Any leather there would've been torn and ripped apart long ago. They like to kick while throwing tantrums too.
3rd row - glad I didn't get it... impossible to get to them while the carseats are in... and they have been for all 4 years now. This is no minivan.