I had a flex for a year and a half and switched to the charge HR. I'm tempted to get a zip and alternate products between everyday steps and work and better performance data while I'm working out with the HR to track time in cardio zone, etc. How accurate is the zip versus other devices? I'm just not sure how it could be as accurate just sitting still and not being on my wrist as I move. Thoughts on the "downgrade" anyone? Will continue to use HR but really want to use my pretty watches again, etc.