Hi Götz,
Actually both drones use the exact same camera hardware (20MP). What makes the RTK version about 4X more expensive is that it can tag each photo taken with GPS with an accuracy down to within a cm or so in terms of vertical and horizontal location in the sky …apparently. Normally GPS with a device like a phone is accurate within a few metres, so this big leap in accuracy is what you are really paying for (survey grade accuracy). The question then is if Reality capture can make use of this exact location of each photo taken and how much better if at all the end result models are.
The hard way to find this out is to purchase the Phantom RTK drone and try it with Reality capture, but its an expensive experiment! 
Does anyone at Reality Capture know if such accurate location metadata associated with each photo is taken into account by the software? This could be a first question to ask. Thanks.