I agree with Undisclosed #2. The use of double poll , double throw DPDT should be considered here. If you have a contact need for access control and a intrusion panel you may want to use 2 contacts or a DPDT contact.
Yes. The double throw means it can be normally open or normally closed. If it were a double pull, single throw it would only be normally open or normally closed not both; although I don't think I've ever seen a door contact that is DPST.
The double pull means there are 2 independent circuits that can see the state change. It's important to note that while both circuits are tied together and will see the same state change, they are independent when it comes to being normally open or normally closed. Also because they are eclectically separate they can both have their own resistors in the circuits so one system can be NO with 1k Ohm in parallel and the other could be NC with 100 Ohm in series.
It is not difficult if you install them regularly, like yourself, or if you have experience recessing door contacts in intrusion work, but for a novice getting the top and bottom halves lined up can be tough.
Also, making basic alignment measurements can be a challenge if the door itself is out of square or unaligned with the frame.