Nice aggro with no damage for low mana with a reasonably short recast delay. They are reasonably serviceable for pre mez break aggro for grouping as well as being very nice as an off tank method for raiding. A good method of "off tanking" during raids is to use non damage aggro (pally non DD stuns AND these spells) from your knight tanks to build aggro on a mob to keep it from beating on healers / debuffers until it can be mezzed. If used correctly it allows a shadowknight to grab aggro on an add and take the hits from said add until mez hits with no chance of breaking the mez. Darkness is useless for that, lifetaps are useless for that, melee is useless for that, heck almost everything else in a SK's ******* is useless for this type of thing either from long recast times, high mana cost, or causing damage. Before this spell line was added, there was no way an SK could do this job. Another use for non damage aggro like this is for kiting non mezzable mobs. Many raid targets require mobs to be kited that would normally summon if damaged and hit too hard to be off tanked instead. This spell line allows SK's to be used for this -- considering the typical method is to have rangers snare these mobs (no damage and good duration) then have paladin's use stuns to hold aggro without damage for kiting, this spell line allows SK's to do the same job as the paladins.
This spell line is very usefull for a raiding Shadowknight so don't knock it till you've tried it. =)