The main selling point for me is the low-light performance. I have other cheaper cameras that work fine for me otherwise. But they tend to produce very noisy images at night, even with their IR illuminators on.
On the other hand, the Dahua starlights I have in some of the same locations even stay in color mode with better images at the same time.
It is the same with digital photo cameras. If you want good low-light performance, you end up needing to spend more for units with better (and often larger) image sensors. A lot of what you pay for in any digital camera is the sensor IC itself.
Then there is the image processing, as well. This can have a huge effect on image quality. Again, you pay more to have faster, more powerful processors, RAM, etc.
Faster, better lenses also cost more.
But there is a lot of competition in this field. And new models appear all of the time. Better and perhaps cheaper cameras are and will be coming out. So like any other high tech gadgets, you have to constantly stay up with reviews and try to get the most quality for your money.
Right now, for low light, people seem to be preferring the Dahua Starlight models. But that could change at any time if someone comes out with even better/cheaper units.
Often, the very inexpensive NVR-camera kits seem quite attractive. But there are usually annoying tradeoffs. And considering the labor you'll put into mounting everything, running cables, and getting it all to do what you want, sometimes the money you spend on the hardware becomes rather insignificant, especially if the end result is poor or doesn't do what you need. Re-buying it all, and reinstalling everything is not pleasant.
Usually, you won't discover the downsides of a system until you have it installed and get some time to use it. That's where research and advice from people who have already been down that road can help a lot!
So it does make sense to research everything first and try to get a system that you'll be happy with on the first try.
