This ring have 3 freeslot for you to imbue in order to match with PVP or PVM.
Although Crystalline Ring and Compassions Eye have spell damage increase 20, the other property is not very good enough or may not suit for your desire armor. e.g. crystalline ring is not suitable for pvp as it has skill increase which make the pvp spell damage increase cap at 15 instead of 30.
Besides, for those who want to make a "high spell damage increase" for pvm ( i made a set of armor with old spellbook that can achieve 94% spell damage (Full resist, HPI 25, Mana Regen 21, LRC 40, DCI 45) . The effect is almost always using super slayer spellbook). This ring is a very very good choice !