Here's how the lock works: there is a shaft that's connected to the lock cylinder. The shaft protrudes up through the grip frame into the bottom of the trigger mechanism housing.
When you turn the key, the shaft turns and blocks or unblocks the trigger mechanism. In "blocked" mode, a metal tab protrudes from the backstrap of the gun to serve as a tactile indicator.
While locked, magazines can be inserted or removed, and the slide can be operated normally. The only difference is the trigger can't be pulled.
As to your original question, any additional safety mechanism increases the chance that something could break and render the gun inoperable.
I haven't personally heard of anything like this happening, but I don't think there are very many Glocks at all that are equipped with this safety system. They've only been making it since '02 or thereabouts.