so that means then if this the case if one drive did then fail later on down the line years to come I would then have to move all the data to elsewhere off the NAS and then move it all back again
No, that is the big advantage of RAID 1, both disks are identical and when the RAID array information is stored on the disks at format time you can have a disk fail sometime in the future and just replace that disk and the array will be restored to the two disks again without you having to worry about data loss. It is that initial setup and formatting that allows this to happen.
All of our NAS boxes are setup as RAID 1 (even our servers but they are hardware RAID) and we always setup clients with RAID 1. Over the last 10 years we have seen a few disks fail but the data was secure and the array rebuilt without problems when the failed disk was replaced.
On separate disks with you copying data from one to the other you have only to forget to copy one important set of data and you no longer have a full backup.
With RAID 1 that copying is taken over by the NAS firmware so that each disk is an exact image of the other. As an example of that we have a client that had a need to call in the police and the police needed to take the original disk with the data on it as evidence. The client powered down the NAS, pulled one disk and gave it to the police. When they powered it up again it reported a degraded RAID array, we supplied a replacement disk and installed it, the array was rebuilt without problems.