It's mainly decent for aeing. The procs can stack on eachother and get multiple +hit effects. The real downside to the proc is just like you say, it takes a resist to get it to go off. It's nearly 100% worthless for fire, because it doesn't proc off partial resists (and full resists in a real raid gearset / spec is pretty rare, back to back is crazy rare). It's better for frost, because any resist is a full resist and will proc the spell; but overall the proc is pretty lackluster outside aeing.