Based on stats alone,
Randuin's (the 'goto' defensive item), 96% efficient
Rylai's (the sort of AP equivalent), 112% efficient
Mallet, 89% efficient.
I think Frozen Mallet just leans far too heavily towards the defensive side. Fighters don't want it, because the ad is very small and health by itself is not good enough, you're much better off as a fighter buying a single defensive item that includes both health and resistances. And tanks don't want it either, because they're not bothered about the AD and the have enough CC already with out the passive.
What they need to do is make it more towards and offensive item. If it had 400 HP and 60 AD, that would make it 98% efficient (without the passive). This would make it much more attractive to fighters, and put it much more on par with Rylai's4. Both would give 400hp and about 80% of the AD/AP of the big ticket offensive items (e.g. infin edge and death cap).
At the moment, it just doesn't have a place in anyone's build. I mean, when was the last time you saw anyone buy it?