How easy and reliable can the A129 pro be mounted or removed with the new mounting system?
The mount is the same as the A129 Duo except for the electronics.
It appears to be very easy and reliable, I've not heard of anyone having reliability issues with the A129 Duo mount, only issue is that the rear camera plugs into the front camera, not the mount, so if using a rear camera then there is a cable to unplug, if not using a rear camera then you can get hold and slide it off the mount in 1 second, putting it back needs careful positioning so 2 or 3 seconds.
Is such a solution supported by VIOFO that I can send an AV signal to a smartphone via WiFi? An example of application would be to stream the image of the rear camera from a caravan or a camper van to the smartphone.
Yes, there is an http stream available that can be streamed to most web browsers and video players.
Only issue is that the wifi must be on, and that increases the power consumption and heat, and possibly new firmwares will automatically turn the wifi off if nothing is connected. So if you need to connect up to reverse your caravan then it is feasible, if you want a permanent rear camera display or one that pops up everytime you select reverse, then maybe not so sensible.
You can get reversing cameras that are designed for the job and are quite cheap.
Another option is to install one of Viofo's MT1 (motorcycle camera) in the rear, it is not 4K but streams nicely over wifi and doesn't have temperature issues since it is dual remote, with a DVR box that doesn't need to sit in the sun.