Unless there has been some serious mistranslation, then this gem skill...is completely and utterly useless...
For starters, the save gem won't break itself, so if you die you won't instantly come back to life(putting it in a mithril box that nobody else can perceive all but guarantees you'll remain dead.) so you need someone to trigger it for you in the case of your death.
Second (again if the translations is not messed up), it's a fucking useless skill...if you break the crystal you return to the exact time and place you created it with no memory of what happens after its creation, all but guaranteeing that you will be forever stuck in a time loop where you will be unwittingly making the exact choices over and over again leading to the exact same unaltered future where you or someone else will break the crystal...
The only way this skill is a "cheat" is by cheating the owner from a skill slot that could be used for an actual useful skill.