I’m ok with it being one shot permanent as I won’t be using it on any valuable endgame tweaked gear (because I don’t have any). However, I absolutely would throw it on my favourite level 4/15 items, where I can just farm another if I get something too bad.
I like the risk-reward idea here. You could use it on your best gear to squeeze out even more power, but at the risk of getting something detrimental.
It’ll be a decision you make knowing the consequences if you get unlucky.
I’m cool with the idea of there being other, more expensive, decks that restrict the possible curses. That way you can make a trade off between more curses of random flavours or fewer curses that are more likely to help you. I would say these decks should pull from at least two “pools”; eg decks for: melee+spell, defensive+ranged, tactics+melee, ranged+skills, etc, etc. They can have special names like deck of the battlemage, warrior, priest, etc.
As others have mentioned a lot of the so called “curses” are positive only, it would be more interesting if the “greater” curses had penalties (randomly selected or static) associated with their greater power. The minor curses may have little to no penalty.
