much more expensive
more secure and more difficult to pick, usual methods do not work
easier to master-key. if you look at the detainers you will see they each have a little slot in them.
If one of the detainers had two slots, it could be operated by two different keys, which were identica,l except that one would use the higher slot, and one the lower.
If each of the two keyholders had another lock, which only had one slot in that detainer, they could both have a key which would open their own lock, and the shared one, but not each others.
Detainer locks can have quite complex suiting arrangements, where everyone's key opens the front door and their own door, some of the people in one department can open any door in their own department but not in anyone else's, some can open certain doors in their own department but not all, some can open any door in any department.
the same design is used in Butters system locks which are a less expensive range that was (might still be) made by Union, and was popular in large offices.
p.s it is also more difficult to copy keys, as they have to be very precise. I have had cases where a copy key would not work and had to be returned to the service centre with the lock to be made a more precise fit.
In my own house i too Chubb lever locks on the secondary exteral doors, and a Chubb derainer on the final Exit door.
OOI, the bolt size on British Standard locks (the lever ones) was increased a few years ago, it is now stronger, and more dificult to lever the door and frame apart enough to open it. However the detainer locks still have the old size
I do not know how this might affect an insurance claim if you fitted them from new. usually you are not required to upgrade your existing locks when the standard is revised.