Why does it have 1 day cooldown? I like these little things, even though they arent used most of the time, it feels nice to have an option. I really miss summon tinker for my guardian, why did they remove it...
I think the reason is economic. Once you could repair with mithril, the in-game ability to do so was bound to degrade. I don't like it either. Honestly I'd rather be made to pay to play, and have all this nickel and dime bullcakes removed. But I don't make the rules.
There is also a weaponsmith anvil recipe. That might at least double your output.