Hi, there is an app call Health sync. You can transfer your steps and other data from Samsung health to Fitbit and Google health or verse. You do have to pay $1.00 but it's for a lifetime. I've been using this app for a couple of months; the only problem I've noticed is when it comes to Fitbit challenges. It won't allow my steps to sync to the challenge. In order to get around this issue, you will need to have your old Fitbit device charged and connected to the app. I'm going to get the new Active 2 and I will see if I can find more ways to work around matter.
P.S. No, you do not need to wear both devices but when you want your steps to sync for "challenge purposes only" you need the device charged and around your phone. Also, do automatic sync for both devices it will make things easier.
