I debated posting because it felt like shitstirring. I think overwhelmingly what you're doing is right. And if a remote power on eg WOL works on the device, so much the better. If I could wish for one thing, it's mods to code or documentation of how to handle drive power down on zfs. The rumour mill is zfs doesn't like spindown.
What is there to handle? I have a ZFS array that works just fine with hard drives that automatically spin down. ZFS handles this without an issue.
The main gotchas tend to be: if you use the array for many things, especially stuff that throws off log files, you will constantly be accessing that array and resetting the spin down timers. Or you might be just at the threshold for spindown and you'll put a ton of cycles on it as it bounces from spindown to access to spin up.
For a static file server (rarely accessed backups or media), partitioned correctly, it works great.
I did try using HDD spindown on ZFS but I remember (It's a long time ago) that I encountered too many vague errors that scared me and I just disabled spindown all together.
