I'm currently using a brodit which is actually for the clubman and fits on the right hand screen pillar - worlds really well - I think it may fit the F56 but not in mine as I've specced HK speakers so will be looking for an alternative
I just got the iOttie flex 3 from amazon. It has a suction cup that is also sticky, and I was worried about mounting it on the dash and causing a mark, as there are some photos on amazon that show this. So I found a good spot on the top left of the big center circle. Even though it is curved, the sticky cup fits well, sticks well, and is in perfect position. I can snap a pic later if you are interested.