The rubber mat is actually not too bad and in the end I've decided to keep it. It fits very snugly, it's rather heavy so it will not move and it has a non-slippery surface (compared to the all weather liner sold by BMW/Weathertech). The non-slippery surface makes it ideal if you have a pet. It has also the cut-outs marked for the bar, you just need scissors or a knife to cut the mat.
My mat came with some type of light colored stains on it, that's why I initially didn't like it. However, as my X5 is used in business, the trunk area gets dirty fast, so the stains don't bother me anymore.