Your average thief has more important things to do than take revenge on things he can't break: like breaking in to someplace easier.
As such, the problem in security is very rarely to make theoretically unbreakable things.
"Do you think you're faster than a lion?"
"No, but faster than you."
For some locks that are critical means of access, you are concerned that they could be vandalized (using cement, for example). Not by thieves particularly, but delinquents taking out their frustration on you. There are ways to prevent this such as the Geminy Shield.
The problem a lock is supposed to solve is the
conditional access problem: to make it infeasible for anyone without an authorization token (key) to gain access, while it is simultaneously easy for anyone with the key to gain access. One of the consequences of this requirement is that the space of possible keys must be so large that no one can simply collect them all. It's for this reason that lock systems have many mechanically independent interacting elements (pins, discs, etc). A single element cannot differ in enough ways to create a secure key system. A second consequence is that the nature of the required key cannot be discoverable from observing the lock: or else you could just fabricate whatever shape was required for each lock. That is called
decoding or
impressioning. A third, easily overlooked, consequence, is that the authorized key must provide access easily. Keys open locks with effectively no force.
Keyed-fasteners like the dodgy "KeyRex" fail as conditional access devices. There is only one varying element, whose shape is easily visible, and which requires force to remove even with the correct tool. If the goal is simply to prevent vandals from damaging parts of a building, one-way fasteners are all it takes, not exotic keyed-fasteners. The product does not solve any actual problem.
There are some limited areas where a keyed-fastener system makes sense, despite its inherent limitations. One of its wins has been for
bicycle wheels and seatposts, where you rarely need to access the fastener, but it's hard to otherwise secure the item—a typical bike lock can't secure both wheels and the seat at once, so some additional protection is needed. This system uses an ellipsoidal recess, so it can't be easily turned using a center punch, spanner bit, etc. That shape also gives it very low torque for its size, which explains why it hasn't been successfully scaled down.