Haven't used the 6TB model but Reds in general do a pretty good job. They have a higher DOA / initial failure rate compared to enterprise models but once they are running, they seem to be reliable. So I recommend just stress testing them when you first get them.
With 6TB drives, traditional RAIDs can be a bit worrisome because of rebuild time. It could take up to 2 days to rebuild and that puts a lot of stress on your other drive in the mirror. That is why many are moving to double, and even triple parity systems with the larger drives. Especially triple parity, aka RAID7 or RAIDZ3. RAID10 or RAID1 relies on one drive to rebuild from in the case of a failure, if that drive fails before or during the rebuild, then you lose your entire array. Double or triple parity systems can handle 2, or 3, drive failures anywhere without losing any data.