In the broadest terms they do the similar thing in a similar way.
There are differences. in general many manufacturers have basic systems and advanced systems hard wired and wireless.
However if you want a camera pir then not all brands do them and these days they tend to be wireless systems and some are capable of short video.
Some systems have automatic frequency hopping in the event a radio frequency is causing problems others just try and pick a clear channel on the day of the install.
Always start with a list of what you would like the system to be able to do.
If it’s diy there is a fair choice of equipment out there and depending on your needs will depend on what is best suited for you.
Then getting into the nitty gritty of detectors and there function not all detectors are created equal.
so you could look at a dual element, quad element, dual technology to name a few of the common types of detector.
Even the same manufacturer has different models and these vary in price and functionality.