I think that's half the problem - WD aren't being transparent about it.
FWIW, I've got a bunch of the 10TB EFAX drives, specifically the WD100EFAX-68LHPN0 (oldest from 2-3 years ago), and none of them are SMR drives, at least as far as I can tell; none of them support TRIM or have large caches and their performance during heavy writes/rebuilds is adequate.
Even if WD were being transparent about it - SMR, at least in its current incarnation, doesn't belong in a range that's historically marketed towards general RAID usage IMNSHO. Random writes, sustained writes and especially parity rebuilds all seem catastrophic to performance.