`zfs allow` on NetBSD - what other perms for mounting FS created with `zfs create`?

I'm currently playing around with delegating certain actions to ordinary users
using `zfs allow`, after having changed permissions on `/dev/zfs` to be 666
(instead of 600).  I realize this is NOT currently supported, but I'm trying to
learn how it all fits together, and what the differences are with ZFS on other OSes
(FreeBSD being the most closely-analogous candidate)

Anyway, some of the stuff "just works", but I'm having trouble *mounting* freshly-created
zfs file systems:

test-zfs:riz  ~> zfs create rpool/home/riz/workspace/foo
cannot mount 'rpool/home/riz/workspace/foo': Insufficient privileges
filesystem successfully created, but not mounted

...looking at guidance from FreeBSD, I assumed it might be because `sysctl vfs.generic.usermount`
was set to "0", but even after setting it to "1", the same error persists.

What should I look at next?  (This is on NetBSD 11.0_RC3)

This is what `zfs allow` shows for the dataset in question:

test-zfs:riz  ~> zfs allow rpool/home/riz/workspace
---- Permissions on rpool/home/riz -----------------------------------
Local+Descendent permissions:
	user riz create,destroy,mount,receive,send,snapshot

Thanks!
+j