Found the fittings that screw into the carpet kept coming out, cured ----now held back with cable ties onto the seats. Absolutely no trouble with mats moving forward now. The BMW carpets are really hard wearing , and in a 5 series I often steam cleaned them, not the little household unit, but the one in the plant workshops. In the X1 I use rubber mats in winter and "posh" mats in summer.The problem with the cheaper mats, although they look good at first, is the anchor holes tear because as you get into a sports car you have to support yourself by digging your shoes into the carpet as you get in, and out up to a point. The point where your right heel works soon deteriorates as well. I would have put these points earlier but was at work. I certainly wouldn't waste my money on them.
Tony.