Mostly they are not very useful, especially inside the house. Light pollution, limited viewing field, fuzzy optics that require adjustment make them more trouble than they are worth.
I have a decent night vision scope mounted to my rifle for exterior use at my place out in the country, it has a quick disconnect and an IR flashlight mounted. There are no close neighbors so the only light pollution is coming from my house or cars from the highway about 100 feet away.
The laws of my state allow me to defend my property at night if necessary and the police response time is an (optimistic) 30 minutes. Still, it is really only useful for a couple of scenarios:
- Observation of potential threats from inside if the power is out
- Home Defense outside if the power goes out completely and the solar lamps are drained (say after 2AM)
- A threat beyond the range of the pools of light around the main buildings (although why I would bother I can't imagine, it would require a really strong motivator to make me confront a threat off in my woods)
- Night varmint hunting (put on the .22 and adjust)
The biggest problem with NOD's is the lack of capability to provide PID. Is the man with the gun the police coming to help or a threat? Most 1-3G viewers don't provide enough detail to ensure that.
Proxima est Mors, Malum Nullum adhibit Misericordiam