Hand of Reckoning is a spell; it can't be cast when silenced. Prior to Patch 4.0.1, it had a 17% chance to miss raid bosses (in contrast to the 8% chance to miss boss mobs for melee attacks). Prior to Patch 4.0.1, even if you were melee hit-capped (263 hit rating at level 80), Hand of Reckoning's chance to miss was still 7.0%.
Before its introduction, this taunt was widely-requested due to the somewhat complicated use of [Righteous Defense] at that time.
Patches and hotfixes
Patch 7.0.3(2016-07-19): Reckoning renamed Hand of Reckoning.
Patch 5.0.4(2012-08-28): Hand of Reckoning renamed Reckoning.
Hotfix (2009-08-08):Hand of Reckoning is no longer able to be used on targets that are immune to taunt, including players.
Patch 3.2.0(2009-08-04): Redesigned. Now does damage only when the target does not currently have the caster targeted, but damage done increased to 50% of attack power, occurring after the taunt effect is applied.