The convertible I own is a 2010 model with 120,000 miles. The vehicle has had servicing on an annual basis or at intervals of fewer than 6,000 miles, on occasion, from the principal dealer. From inside the vehicle, you can hardly hear the engine running at idle, and it's as smooth as butter.
With a 2009 model year or later, you should not be concerned about balancer shaft concerns. Engines with serial numbers 30 468993 and after have upgraded components installed to fix the issue.