It's a used gun. Shop the price.
It was purchased, shot, and the previous owner decided it wasn't his cup of tea. Why? It wasn't cheap, and he couldn't sell it new, so what was it that wasn't what he wanted so much he lost money on it?
It's a proprietary piston gun. Nobody carries parts except the maker, single source only. Even if you shoot 1,000 rounds a year thru it, will you be able to buy parts for it 5 years from now? Other piston guns have already gone out of production.
There is a lot of hearsay, speculation, and outright rhetoric thrown around on the subject, but nothing nailed down - what does this gun do that is numerically superior for the money? $1,600 would get you a Noveske, and you'd be just as well served.
The price jump from Stag to Para is a serious one. What is the real money based budget figure? Spending $1,600 would mean about $700 won't be available for an optic, ammo, etc. And honestly, most shooters would be ahead with a piece of glass and some experience rather than a safe queen. What do you REALLY plan to do with the gun?
Quad rails are $250 light and laser mounts. Unless the barrel is guaranteed 1/2MOA or less, about $25 in rail strips will net the same effective accuracy. And since an Eotech is primary, the $150 for BUIS could go for another red dot as backup. It's not an issue duty life or death gun - you can get something more effective than irons, that's the whole point of the Eotech. So, don't step down on the back up sights when the same money gets you something better.
Lot's of food for thought.