I (unfortunately) have vast experience with the Voinic brand. I used their products almost exclusively a few years back because at the time, my preferred vendor carried them exclusively. Since that time, I have had exposure to many other lower tier (cost) products and have found that there are usually much better alternatives. The Vonnic line will vary from unit to unit quite a bit. They crowd source their products, so one DVR will be Chinese based with one UI and set of apps, then the next will be Korean with its own UI and set of apps.
The main reason why we no longer use their products is we would have clients call for support, but we couldn't help them over the phone because we didn't know the menus well enough, due to the fact that the UI was always different. They would also ask for help setting up viewing devices and we would have to refer to a list as to which DVR used which app and for what device, i.e. iPhone vs Android.
If you want a more stable product line, I suggest looking into the Dahua based products out there. Their DVRs are much more user friendly, cost less, and all use the same UI and apps, no matter if it is a basic 4ch DVR or their IP recorders. They all integrate very easily into one app and the interface is the same as well.
If you would like to know where I buy my Dahua gear, let me know and I can recommend a dealer.