Level correlation plays a role on the proc rate because I can assure you it's NOT 15% on high-level mobs.
This is a decent weapon anyway, very useful if you have a support-oriented playstyle, or if you like breath spells without losing TP (at the cost of magic accuracy provided by elemental staves).
Approx 15% proc rate on a drain 7.5% for each type. Kalessa did the testing which can be found here
http://kalessa.livejournal.com/tag/experiments+with+hofud
Hofud is now more or less a transitional piece, it isn't what you'll want at lvl 99 when all the great options are, but when you're at lvl 75 after a fresh Raubahn fight (Or if you're leveling BLU in general) this is still a very nice piece. Make no mistake, despite the randomness of the proc on Hofud, either one will be helpful.
Personally I've wanted this since I got hacked back in '09 because of sentimental values, but in either case I'd also use it for towning (Which is what it's good for when you've got much better options in your inventory).
PS: Looks great when dual wielding it with Tyrfing.