The Precision Reflex Retro Carbon Fiber Forearm comes with a 8.5" top rail, (3) 3" rails for 3,6, and 9 o'clock. It does not come with any other rails.
This Precision Reflex Gen II Mark 12 Mod 0 Retro Carbon Fiber Rifle Length Forearm will not fit an AERO Precision M5 upper. The Precision Reflex Gen III DPMS .308 Carbon Fiber Rifle Length Forearm located at the link below should work with an AERO Precision M5 upper as long as it is not the M5E1 upper.
https://www.opticsplanet.com/precision-reflex-gen-iii-dpms-308-carbon-fiber-rifle-length-forearm.html
Information was not provided to us recommend reaching out to manufacturer.
Yes, it should be compatible.
The Precision Reflex Gen II Retro Carbon Fiber Rifle Forearm attaches via a proprietary barrel nut - included in the package.
A barrel nut is included.