They Have been on here before. I haven't personally seen anyone get them from any of the rocket hub deals ( I know several people who bought into the idea, but have yet to receive them) To me I cannot see how you can produce a metal lower that needs 8 machining operations ( this requires 2 large CNC mills to do. ) for the price they are saying is doable , When the block of material is about the same price or more.
The 7075 billet material is going to cost near what they're "asking" for a finished product. So if you pay upfront, everything else is free? CNC machine time, fixturing, carbide tools, manpower and electricity for the big 3 phase machines? Doubtful. Stay away. The price isn't even close to what it would cost to make one.
The cheapest 80% 7075 lowers out there are forged. Can be had for $100 or less if you search around. Billet lowers will always be more because of the additional machine time.