I have the Millett, Vortex and the Trijicon.
Since your budjet is 600 don't even look at the Millett. It is a good scope for the money, but since you can afford better, then look at something else. Glass is OK, but there is alot of distortion around the edge of the image on 1x. Turrets are crude(don't even click). Reticle is good. Illumination washes out in the daytime, but you can still see the reticle well enough.
Vortex has great turrets and even a rudimentary zero stop. Illumination is great. From NV settings to very bright. Glass is great esp for the money. But there still is some distorting around the edge on 1x. Reticle has ranging/aiming marks for longer distance.
Trijicon is supurb on 1x. No distortion around the edge. Not sure why, but it is easier and faster to get my eye behind it for snap shooting(exit pupil maybe?) The image seems to go right out to the edge of the scope body. On 4x the top of the triangle post is pretty good for precise shots out to 300m but there are no additional aiming or ranging marks on the reticle. Turrets are covered, but I guess you could leave the covers off. Illumination dosn't need batteries, but could be brighter in pitch dark.
So my advice is to figure out how important 1x is to you. If you are mostly shooting supported 1-300 m then the Vortex will serve you well for less money. If you are shooting off hand CQB stuff at +/-50m and occasionally out to 2-300m then take a look at the Trijicon.
Presonally I like the Trijicon the best but that depends on how much the extra $2-300 is worth to you and the other above mentioned stuff is. S&B, not worth the money or the weight. If they start deploying fat middle aged bald men, then maybe. You might be able to get a NF used for 1200 but that will double your budget, and I honestly don't think the 1x is as good as the Trijicon.
GC