can it be used or is it as bad as people make out to be
It has a few applications.
When the enemy hero is bleeding, the hero equipped with the hammer will be able to do more dmg against him.
When you lose a big portion of your hp while still being in control of the battle itself, the hero can quickly turn into a nasty fully critical damage dealing berserker. However, because that does not pierce Berserker aid itself, this effect is pretty much nullified.
In conclusion: it's bad in my opinion.