Do these systems mark when there is an activity so you can easily find the incidents in the recording? What is the best way these systems send you alerts if they spot someone on your property at night for example?
You can configure Video Motion Detection (VMD) or smart events such as line crossing.
You can use these to mark the timeline.
You can configure the system to send you email alerts and/or push notifications to an App on your phone.
However, it is very hard to perfect detection.
You tend to get lots of false alarms; birds, spiders, cats, clouds, moving bushes, leaves, etc.
You probably won't want it notifying you overnight.
Maybe getting some 4MP Dark Fighter cameras is budget friendly then upgrade one to the 8MP variant when they come out. I can use the 4MP one in a less important location then.
NB - it is available in two different focal length ranges; most people need the 8-32mm variant, the 2.8-12mm is only suitable for close to car applications e.g. alongside an entry barrier.