That can't work on deadlocks, or can it? A popular lock in the UK is the Avocet:
...very popular and used on many doors - the problem is there's an "Avocet Opening Tool", which can be sold to anyone, which allows anyone at all to open it within seconds. I almost bought one, till I saw that opening tool for sale...
Doors secured with these locks are still open to all the easy opening tools, as the ones I mentioned push back the bolt in the door lock, nothing to do with the cylinder at that point.
Double locking does involve the cylinder, and some cylinders are more difficult to pick, but electric picks can usually open most.
The lock you mentioned, is supposedly difficult to break in the middle, as many thieves, especially if the cylinder is a bit too long, grab hold of it with either a clamp, or special lock breaking tools (very cheap) and simply snap the middle of the cylinder, pull the outside part out and push the inside part into the house, then using a special shaped plastic "key", then simply open the door!!!
This guy is SLOW! 42 seconds to open the door:-
This guy is doing it from the inside, which is really easy, but both inside and outside can be attacked. The qulity of the cover surronding the cylinder plays a large part, and setting the cylinder back in the door, instead of flush, makes it even more difficult for the burglar:-
Electric Pick guns being demonstrated:-
Regards to all
Andy