I must admit that I didn’t investigate the MAVLink interface very much but I believe that it, like the Siyi’s implementation, simply uses MAVLink as a replacement for SBUS. So it simply pulls the RC stick/switch/knob positions from the pilot via MAVLink. This means that the gimbal can’t be controlled autonomously (e.g no ROI, etc) if MAVLink is used. Using the serial interface, AP can control the gimbal even in autonomous modes