There's no problem mixing the TZ touch and NN3 systems. One thing to consider is that the NN3 display will have to remain the master in the system. Because of that the NN3 display will have to always be turned on. The NMEA2000 network redundancy will not be utilized to its fullest with the mixed system. The system ids of both systems can be linked so that if you purchased charts for your NN3, you won't have to purchase them again for your TZ touch. Hopefully this addresses some of you concerns.