Yeah, I promise if it's real 3M VHB tape it'll come off easily enough when it needs to. I had one on my previous dash (matt obeshe, I'm sure I'm spelling this wrong) for the best part of 3 years, and it left no mark when removed. Recently I've been trying all kinds of devices on by carbon dash, and again, there's never any mark or residue left. On the flip side, I just moved a mount in my wife's Q5 that was stuck to the soft trim, and it has left a small mark, so I'd always stick to the smooth surfaces.
The option of using the airvent mounts doesn't really work in S & X, due to the overhang of the top part of the dash. Plus in the summer I need all the vents at full tilt, so it's not a great option regardless.
We'll have a Qi-enabled charger for sale within a week, it's compatible with our existing mount, so if you already have one of those then it's a trivial replacement (of the magnetic mount with the new Qi-enable micro-suction mount), otherwise it comes with it's own mount as well. Qi charging doesn't play nice with the metal plated needed for the magnetic mount, so we had to find an alternative solution.