Every 3rd party keyboard (e.g. all keyboard apps that are not native to the phone), will need "Full Access" to function. 

Your smartphone will notify you during the installation of the Neurokeys app, with a generic message, that Full Access is needed. 

Full access allows us to collect data from anonymous keystrokes and to transmit this anonymous data to our secured servers. Without Full Access a 3rd party keyboard like Neurokeys won't be able to function.