It's all about quality. Usually you get what you pay for. I have been selling cameras for 26 years and found the only way I could ever determine a difference from one to another was put them side to side and switch back and forth. The specs often didn't mean a thing, and usually price determined the winner.
I guess, this is near impossible to do with the packaged systems.
I don't like many of the packaged systems because they use goofy, specialized cables and connectors, rather then industry standard coax or BNC connectors, or CAT 5. They often use fragile (cheap) skinny wire, and if you are five feet short, you have to buy a fifty foot pre-made cable and roll it up.