Well, I can tell you guys my story. I shucked 6 x 5TB SMR (shingle) drives from that Amazon Seagate Expansion External HDD deals back a year ago. I have been using these guys in both Illumos and BSD (Freenas) ZFS. I finally switched to Freenas 9.10 which has been running for about a year now. The SMR drives are installed in a SuperMicro chassis. This Freenas box has: mirror zpool, decent amount of RAM (64GB), fast Intel SSD for ZIL, and 10GbE SFP+ nics.
I use this system at work for all of the following workloads running simultaneously: lab/dev VMware VMs, Veeam backup repository, and SMB shares. I do Veeam incremental backup every 3 hours and full once a month of our live Production environment to it. Additionally, I would do Veeam replication and backup copy job from it too. So, a fair amount of data is moving through it all the time.
It's been running just fine for about a year and just recently one drive developed 16 bad sectors which ZFS/FreeNas had no problem dealing with in terms of marking them bad and continued to hum along. I have not even replaced that drive yet, and my Freenas ZFS box is running along just fine. Scrub found no issue with my pool. I will replace that hard drive soon though.
As for speed, like everyone said, once the cache is used up, it can be slow down to around 30 MB/s and the speed is inconsistent where no logic would make sense. I would sometime fill it all the way up above 80% due to monthly full backup, and this would slow it down quite a bit as ZFS doesn't like it above 80% capacity.
Anyway, as you can see, these shingle hard drives are actually not freaking bad at all. You just have to be aware of the drives' limitation and not expecting them to work like the normal 720o rpm drives.
I'm planning to get a single 8TB one for home backup. I don't care about speed as the backup will run overnight in the background anyway.