I vaguely remember reading somewhere (may have been on this list) that
putting anybody in the disk group is a big no no, I think it was to do
with security.
*It is* (shoot foot material). So is setting ntfs-3g setuid. Which is
another practise used for what the OP wanted to achieve - in the way he
wanted to do it.
Like sudo no password it's a common practise - in hindsight I should
have refused to help with that option (I did suggest udev) - and there
are other ways.
Whether I'm misremembering or not it would be nice to get it cleared up.
You didn't misremember it - unfettered access to raw disks is not good
practise.
I was wrong. Following those instructions could have caused the OP to
inadvertently break Windows.