The fact that this ring has -75 Fire doesn't matter at all. It doesn't increase the damage you take from Fire spells, just decreases the likelyhood that you will resist them. You won't be resisting any Fire Spells/TP moves without a decent Fire Resist setup anyway, so unless utilising a Fire Resist setup this ring is a good option.
This ring is awesome for HP builds and the like the -75 Fire Resist is iffy maybe but hey if a mob is going to use a fire based tp move/spell it should be common sense to take it off anyway lol i personally use mine for heat breath and PvP :D, and +75 HP is alot for its lvl if you got it and want to wear it go for it.
Why are you voting down Beliash? They are 100% correct in everything they said, the -75 fire resist will not make you take any more damage from a fire spell, just decrease your chances of resisting it.
I might have to disagree with Beliash on this. With this ring on, two I.R. pieces and a Lamian Bow I was getting hit for around 1100 DMG from Firaga 3 in Campaign, without it I was getting hit for around 600. So obviously less resistance is going too equal greater damage taken.