OBDI codes on a Ford, a piece of jumper wire will tell you as much as any code reader. I think you are wasting money on code readers. A scanner on the other hand is invaluable as you can get a data readout/log to actually help you diagnose a condition properly. A trouble code is just the beginning of a diagnosis, any schmuck can pull codes as AutoZone employees have demonstrated.
As far as OBDII scanners, verify it supports the proper protocols for your vehicle. Few generic scanners support the manufacturer specific protocols/busses, some do. Once again, having the ability to have a data link to read sensor outputs/PCM outputs is invaluable to a quick/proper/correct diag.