Huh it looks like European cars often use larger sockets (learn something new every day). Meanwhile I found the original review that stuck with me. By design the charger uses a center spring that's too strong and forces it out of the socket a little bit.
There are a variety of other critiques (e.g. came apart in the receptacle and "All of this could have been avoided if Anker would have angled the leading edge of the side electrical connections more.", "The catches on the side of the charger won't release like the traditional spring ones do.", lack of fuse) as well.
* Size A: inside diameter ~21.0mm (mainly American cars)
* Size B: inside diameter ~21.5mm (mainly European cars)
https://en.wikipedia.org/wiki/Cigarette_lighter_receptacle