OK, so I bought one of these a couple years back for my father to o use on his motorcyle. He sold his motorcycle so I reclaimed it and have started using it on my GTS.
Here's the deal. If you are someone who wants to take a drink along with you this is the best way to go. I pop it right on the rear cowl, put my drink (with a lid on it) in and take off. When I get where i am going, I take the drink out, pull off the Magnetic cup holder and put it in my top case/under the seat and I'm all set.
Its made very well, the magnets are very strong. I've had no problems with it moving, shifting etc. If you guys are interested, I'll post some pictures.
https://www.imcuniverse.com/store/magcup.htm