Ulthuan

I have been away for so long that I have lost touch with many concepts.

The Shield of the Merwyrm grants a 4+ parry. But if I remember correctly it was always the case that it was only when you use a standard hand weapon that you get parry.

Normal parry saves require a non-magical hand weapon, yes. However, the shield of the Merwyrm's entry specifically states that the 4+ parry save functions even with a magic weapon.

Indeed. However, do note that the other parry rules still apply. So it's only on foot, and only when attacked from the front etc. Which makes it less good than it appears