Depends on what you're doing and your confidence in navigation, equipment, group, etc. I run two separate odometers, one in my Polar and a Cateye. I've had them both malfunction or get reset on various occasions for various reasons. I can't imagine how you'd find the next control and/or stay on route on a long permanent or brevet without an odometer. We carry two or three headlamps, two tail lights, two tubes, a spare tire, extra batteries, extra spokes - none of which will help if you don't know where the next turn is. Retracing your route in the middle of a long brevet is not a morale booster. So I vote for redundancy.