The locking turret is nice on the ATACR but not necessary. All my ATACRs at work lock but my personal scopes do not. Those turrets will not easily move on you with either sight. The ATACR will have a more forgiving reticle viewing area and the 4-16x42mm is one of the best scopes made. The 1-8x and 7-35x are too. Everything else they make is good but those three are awesome.
The NX8 is a bit of a compromise optic, as there are no free lunches. The reticle viewing area is a little more critical but if your gun is well fitted to you and you mount your scope properly then it's a non-starter for me. The image will not be quite as good at higher mag compared to the ATACR but it's a sight, not a viewing device. The advantage goes to the NX8 though if you need to shoot inside of 45yds with magnification (I use it for rimfire). The only NF I've ever sent in for repair was a NX8 4-32x and it's dude-focus/parallax was out of spec. It was a very early production model and they had it back to me in a week.
Aesthetically, the ATACR looks better on a smaller gun and the NX8 looks better on a longer gun.