Note... we design, manufacture and benchmark 'software agnostic' NVRs, Viewstations, and Storage solutions.
Beware the claims of these low cost systems. Be sure to do your own testing on them.
One thing I have noticed (and tested in my lab) is that the supported channel count of a 'low cost' NVR is not based on any defined performance/quality metric. One system I had in the lab claimed 16 channels and 320mbits support. In real testing I got 10% of this claim. The 320mbits was a combo of Input + playback + Live NIC Mbits. We even bumped the supplied CPU up to a maximum supported on the mobo used and still could not get near the amount.
Another thing to pay attention to is the NIC hardware used in them. My lab tests have proven that Intel NICs are more robust and performance enhancing than the other NICs used. This is important if your total bitrate from/to the cams and viewstations is 100Mbits or more. Between 75 and 100 is a crap shoot.... be sure to beat on the non-intel NIC with this rate. Less than 75Mbits seems to be OK for all types.
A final element to check is the HDD used. All drives will fail over time...and the less expensive ones will fail much sooner than the enterprise class ones. Also, SSD drives for a storage target need to be used carefully. What creeps up on them is the Write Endurance factor.
From the software side.... be sure to check out the camera support for the systems that come with a VMS that is not well known. Many are trying to make ONVIF work...but you will need to validate that yourself.
Perhaps this can be its own discussion, but from what I see and have tested, you do get what you pay for when 'low cost' to too much of the equation.