Assuming that you would never be able to take off said helmet, and there's a fifty/fifty chance you'll end up permanently possessed by Nabu, who uses your body for his own.

In putting on the Helm, you would be taken from this world, with only 24 hours to settle your affairs and an inability to use your magic on a large scale (no ending world hunger, etc) while on our world.

After 24 hours, you'll be transported to a war-torn world in need of a savior. You'll be an alien, unable to return home, and the only thing stopping an intergalactic armada the likes of which would make the Galactic Empire (Star Wars) piss their collective armors in fear. While your possibility to win is about 65%, it will be a long and costly war.

You have this knowledge upon picking up the helm. Would you choose to wear it and become Doctor Fate?

under these circumstances? hell no

This is like a version of Russian roulette so probably not