Regarding the question of retaining zero, Eric of IraqVeteran8888 You Tube channel tried it out ahead of the show and that doesn't appear to be a problem.
According to F&D Defense's promotional information:
F&D Defense’s previous innovation of the 4-bolt lock up system is the prime reason the XAR technology is even possible. By removing the limitations of a barrel nut and adding the XAR folding innovation, F&D Defense has created the most compact, fastest deployed AR rifle in the industry, without sacrificing the reliability, durability, and accuracy demanded and expected. Faster deployment, faster takedown, no loose parts.”F&D Defense will release the XAR Invicta in the summer of 2017. For more information on F&D Defense, the XAR technology, or the F&D Invicta, visit FDDefense.com.
Hat tip to Matthew Moss at taskandpurpose.com