You want cylinders and keys that can be serviced in the field, by your own locksmiths and technicians. You do not want a system where you have to rely solely on a manufacturer or distributor to do your cylinder servicing and key cutting for you. You will want a system that could be completely self-serviceable. This will eliminate servicing delays.

Language to use in key system specification:
Cylinders and cores shall be immediately rekeyable to new combinations or a new combinations or a new system at any time desired and shall be serviceable on location in the field. Installation of the cylinders shall require no modifications to US manufactured commercial grade locksets.