Customer has a 7-unit apt bldg with Titan knobs and deadbolts in a masterkey system. Also has some spare cylinders and rotates the spares into doors as tenants move out. Keeps a log of which cylinder was installed in which apt during which period of time.
I have finally talked him into replacing the Titans with something better. I am leaning towards a Schlage IC, with a half-dozen spares each for the knob and deadbolts.
Quite important in the decision is whether or not the new knobs/bolts will go right into the existing (standard) holes and line up with the existing strikes. This is because the doors (old) have quite an intricate system of draft protection built into the edges.
Of course the easiest solution is to just install one and see what happens!
Ralph