Hi Dan,
Welcome to the Nimbus thread and APM VTOL Plane forum!
Both of those systems are meant for long-range mapping that integrate the radio link and data link into one RF signal. The T12 is a Skydroid system. You can read more about it in the main Skydroid thread. I have the older M12 system that doesn’t have a built-in camera link. It works well. I use it on my Tarot 680 Pro hexacopter because it has the mini gimbal controller on the transmitter to control my pitch and yaw on the hexcopter gimbal. You don’t need this gimbal function for mapping since a gimbal is seldom used in that application.
I don’t know anything about the DA16 system. Once you pick a system, I have found that using other systems can be disorienting. My Skydroid M12 has labels on all the switches because all my other VTOLs, copters, and planes use either the Horus X10 or the Taranis X9D+ as they are similar.
One feature that may be different between these data radio systems and the FrSky systems is the 6-position knob used for selecting one of 6 flight modes in APM. My Skydroid M12 has a 3-position toggle switch for modes and a 4th mode can be assigned to a secondary switch. I don’t think Plane has this feature like we got used to in Copter.
Good luck!