Been using KoKen tools for some years.
Sometimes they win on price, sometimes price for the quality, sometimes they make a product that’s just better than everything else out there. Spark plug sockets are the latter.
They make plug sockets with spring clips that are my all time favourites. I have these in 3 sizes.
The spring clips don’t really work with 12 point plugs, but they offer their magnetic sockets in a 12 point 14mm.
I love their extended sockets, as you don’t leave the socket behind while removing it from an installed plug. Again, there is a 12 point 14mm version.
And for difficult access there are universal plug sockets. Once again, there is a 12 point 14mm version.
They offer another range of plug sockets in their Z Series / Zeal range that offer a waisted design, but I have never encountered a situation where the regular ones don’t work.
For info, spark plugs are generally made with Imperial sized hex’s. 16mm are actually sized for 5/8 hex, and 20.8 for 13/16. What the problem is in giving the correct size, I don’t know.
14mm hex plugs are different. I believe they are actually sized to 14mm, so you won’t find a 9/16 plug socket.
Somebody above mentioned Hazet. They are nice too, nice spring clips, and Hazet will offer something for BMW, but I slightly prefer the KoKen.
I have two BMW’s, but none that use the newer plugs.