Hi
I went from a 2009 Swing to my 2019 C650 (in between was an R12RT). From what I understand there are no big issues with the 2016 on up. That was the year of a redesign with the variator and the muffler being upgraded. Everything else on the bike remained the same from the previous year.
While the bike weighs about the same as the Swing, it handles sharper and has better acceleration as well as a much more pronounced "Growl" to the engine due to the 270 degree crank. It also sits taller, so while flat footing the swing was easy for me, the c650 is about 2 inches taller. Riding position is about the same, still upright and pretty comfortable. Under seat storage is about the same though there is a pronounced hump from the rear fender that limits the size of helmets you can store in there.
All the bikes have ABS. Brakes are not linked. The power screen, heated grips and seat are really nice in chilly weather. Built in TPMS, and some useful info displayed in the dash like MPG, oil status, etc. I don't care for the doors for the cubbys on the dash, they seem flimsy compared to the swing and are not lockable. But they hold enough stuff anyway. There is no hand brake, the side stand locks the rear wheel when it is down. I really dont care for that, I would always move the Swing around with the stand down so it was easier to set it down at any point. With this one I just straddle it while moving, it is a heavy bike and I'm not getting any younger.
All in all its a fun bike. Gets to 70 very easy on the highway, more of a highway machine than the Swing. Maintenance is more involved than the Swing. Besides the CVT belt, you also have an enclosed chain that has its own maintenance requirements including guides that take up the stretch that need to be changed out depending on wear and mileage. If you take the bike to the dealer for service it can get pricey, folks with some wrenching skills can do most of it themselves. In order to reset the service indicator you need to invest about 100 bucks for an ODB2 wireless adapter and an app for you phone called motoscan. That gives you access to the ecu for any BMW bike and lets you set the service indicator and read codes.
Hope this helps.