Hello and welcome,
If you choose the used gun, I would make sure I ordered two new mag springs:$8+ea, recoil springs:$5+ea, grip screws:cheap insurance. Those parts will make sure your gun is running right. If the used gun has the older carbon fiber grips, I would be torn because they are becoming collectible.
Whether to choose the sighted vs unsighted is pretty much your own taste. The sights though small are very useful. I have the sightless model and am totally confident in my abilities with this gun up close.
You might want to check w/Tom @ The Irish Gaurd a local sponser to this site for a good price on a R9.