I guess it depends on how you define "big difference." The 2016 M2 was an amazing driver. The 2017 model is an evolution of the 2016 and it's better in many ways, but we're not talking massive differences. That said, I switched from the 2016 model to the 2017 because the higher MOI makes it more forgiving and it sounded better.
Personally, I may be in the minority that prefers the 2016 M2 to the 2017 M2.
There's no doubt they're both great drivers - I just feel the look @ address, feel, and overall performance of the 2016 was better.