Pyramid brand extender is available at Gateway BMW for about $40. Its cheaper than others because you have to drill holes to mount it. I used an index card template to locate the holes according to instructions and my judgment. Four plastic rivets are provided and according to Tom Huff they should be adequate.
I mounted it when I replaced the front tire because I wanted to ensure a proper installation. The fender can’t be removed with wheel in place on my 2016 1200RT. So far unit works as advertised.