In general, there are many different brand names that appear on what I would call a 'generic Chinese DVR'. Most of these are not all that bad. These can be hit or miss, as they tend to have the cheapest possible power supplies and other components. In some cases these will fail quickly, or run for ten years without issues--that's the nature of cheap electronics. Be sure to first download/test the remote viewing smartphone app, as you don't want to be 'stuck with' a terrrible app. Many of these DVRs only work with the vendor app.
Technology-wise, the technology in use is TVI which is essentially 'digital HD over coax'. TVI is limited to 1080P and I believe that if you need more cameras or to replace the DVR in the future, you may need to stick with only the Defender brand.
These days the more modern technology is IP cameras that use ethernet for connectivity. IP cameras are standards-based so you can mix and match devices, Power Over Ethernet (POE) means the same cable provides power, and the maximum resolution is unlimited. Bottom line is that ethernet is cheap, reliable, and future-proof. Most IP cams sell for about $120 each and expect to pay $50/channel for a Network Video Recorder (NVR). An important consideration is that with higher resolution you may need fewer cameras. So if you use wide angle (2.8mm lens) 3 or 4 Megapixel IP cameras, or even a 12MP 360-degree camera with a 1.2mm lens, for most normal applications you don't need as many cameras.
Tip: if you plan to go with the Defender, it would be wise to throw out the cables and power supplies that come with the unit and buy your own (and maybe the HDD too). While those 'may work for awhile', one or more will die given the slightest power surge.
For example Q-see cables are good: https://q-see.com/products/100ft-bnc-male-cable-with-2-female-connectors-qs100b4pk
I would also get a better PSU for the DVR AND consider a surveillance-rated HDD https://www.amazon.com/Purple-Surveillance-Hard-Disk-Drive/dp/B00IMPO5MO?th=1