Actually it works in 2 ways:
As a debuff on target:
lowering the targets crit resistance by 28 points at lv15 + SPR x.8. Most bosses have crit resist of 120 to get a least 50% crit chance on bosses you will need at least 50 points in SPR
or your could Raise your Crit Rate further through Dex and using Gems
as a Self Buff:
adds 100 + 100(max attribute) to crit attack and 48 points to magic amplification
Crit Monk is actually the best route for monks, since most of the monk skills suffer from low base damage and weak weapons for cleric class, at lv170 swordsman and archers have access to weapons with 250-400 attack power while clerics only have 230 highest from maces and 1h swords
Just don’t go Full Dex, it would be best to achieve most of your high crit rate through gems, buffs, and gears without sacrificing points from STR
I believe a 40-50% crit chance is optimal for monks