I think it's difficult to judge the difference without driving or even owning both My2016 and MY2016.5 models. The rear suspension Watts linkage has been removed on all but the top spec engines (1.6i etc) and it seems some soundproofing has been removed too.
The general consensus seems to be it was a cost saving exercise that has made a small but perhaps not insignificant difference.
In handling is not really much difference. Most obvious will be on highway and on bad roads. Watts link adds 3rd point so it stabilizes the rear axle, so it can use softer bushings. And that means less noise and vibrations from irregularities on the road.
As I understand it I have a my16.5 , I've with no watts link , I often use back roads for work , but noticed even though the steering is smooth the handling is terrible , so I am dropping tyre pressure to around 35 from 42-43 , will let you know