As loong as they will only be doing what they say they will, I don't see any sort of legal trouble they could get into.
The AR15 isnt patented. Dozens of companies make them. These DD lowers are no different regardless of wether they are CNC milled or 3D printed.
Amd just because they are against patent laws doesn't mean they will be stupid enough to start making publicly available copies of patented designs.