I'm not sure exactly what you are wanting this to achieve, but I can tell you that with a $400 price limit, you're not going to get much.
So, I looked at the unit you linked. Best I can tell from the ad is that it is a digital unit. The only other units available in that price range are gen 1. Digital has almost no light amplification ability, it is just basically an incredibly sensitive infrared camera. What this means is that it will need ambient light to see anything. On a cloudy or moonless night, you will see little to nothing, unless you are in an urban environment, where there is always ambient light (except after the grid goes down). It will depend on how good the ir light is as to how you see using it. Usually not much more than 30-50yds. You can get a separate ir light that is brighter and more focused that will extend that.
Understand that when using an ir illuminator, anyone else with any NV will see your light, a beacon in the night.
So, tactically, these have lots of limitations. It's OK in town, with the grid still up, but out in the sticks, or grid down, not so much.
Also, 6x magnification will make using it at close range difficult, if not impossible.

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