While the advantages of ADS-C/CPDLC (or FANS 1/A) are legion, the datalink component is not without its pitfalls that can confuse the inattentive flight crew or one grown complacent due to the automation that characterizes the system.
Ultimately you're going to have to upgrade to ADS-C and CPDLC to operate above FL 280 in most oceanic airspace anyway (e.g., by Jan. 1, 2020, in the North Atlantic), but here's what you're missing out on now in the North Atlantic Track System.
The process of creating a safe, fuel-efficient and regulatory-compliant oceanic flight plan actually begins with the compilation of a comprehensive international operations manual based on standardized procedures and best practices.