Hi @drdevil44 and thanks for your query. Indeed the Tobii Pro SDK Python Bindings are free of charge to download and whilst they will work without issue on the Tobii Pro range of eye trackers, in order to use this SDK with the consumer level of Tobii Eye Trackers (such as the 4C) this will require the purchase of a special analytical use licence which comes with an unlock file that will allow proper operation.
If you are interested in this, then you can read more @ https://analyticaluse.tobii.com/
Otherwise, for interaction development using the 4C, you will need to use our consumer range of SDK of which we have several which you can download and test @ https://developer.tobii.com/consumer-eye-trackers/
I would recommend that interaction library for a quick and easy way to get started. Please do let us know if we can provide any further information.