SMR hard drives are e-waste. SMR hard drives will grind to a halt in array rebuild situations, and you should not use any mechanical hard drive outside of a redundant array if you can avoid it. SMR drives are the worst parts of mechanical hard drives and solid state drives put together. SMR drives are not worth the scrap metal used to make them. Never buy an SMR hard drive. Never let a friend buy an SMR hard drive. Always check to make sure any drive you buy is not SMR.
Hard drive companies will SMR any hard drive they can get away with. I've seen them as small as 1TB even in 3.5" format. They've been sold as NAS drives in the past, and probably still are. I do not wish to traverse WD's product lineup today to find out; also don't buy new hard drives if you're paying for them.
Some of these downsides can be mitigated somewhat with major software behavior changes, but there's a lot of work involved in that (do you enjoy file system tuning?) and I guarantee you can just go buy used CMR drives for less anyway. Less by a margin great enough to afford extra drives in an array.