I rode without these things for years, but rode with a bike computer last year. Fun, but I was constantly checking it, wondering why it wasn't working etc. Wore a HR monitor occasionally, but just putting it on would make my HR rise.
Skipped them both now that I'm not doing any real training on a bike. I like gizmos, but only if they work all the time and don't interfere with anything else.
Winter riding is much less about badassery and much more about bundle-uppery. - malkin
1995 Kona Cinder Cone commuterFrankenbike/Selle Italia SLR Lady Gel Flow
2008 white Nakamura Summit Custom mtb/Terry Falcon X
2000 Schwinn Fastback Comp road bike/Specialized Jett