Hi @emanuelevivoli thanks for your query. There is no difference in accuracy between the Core SDK and Pro SDK although more data is exposed in the Pro SDK such as individual (monocular) eye gaze data along with more detailed calibration feedback, amongst other metrics. You also get access to completely unfiltered raw gaze data in Pro SDK whilst Core SDK has always slight filtering. Also note that headtracking data is not available with the Pro SDK.
The Pro SDK also supports more language bindings (Python, .NET, C++, Matlab) and other operating systems such as Mac & Linux (Alternative OS support for the Core SDK is still in alpha stage and restricted to Stream Engine API). For developing interaction applications, the Core SDK would be your best bet as the libraries are there ready to use for this purpose whereas you would need to develop from scratch for this purpose using the Pro SDK.
If you have a 4C, you would still need to purchase the analytical use licence to operate with Pro SDK so the SDK in and of itself does not give you permission to collect gaze data. Further details for purchase @ https://analyticaluse.tobii.com/
These are the main differences between the two SDK’s, hopefully this clarifies your doubts. If you could kindly describe your intended project, we would be happy to provide further information as necessary.