You guys underestimate the value of the regen on Warmog's IMO. 600 HP vs. 10 Damage or w/e is already pretty lopsided in Warmog's favor, especially since Mog's is cheaper, but that 40 hp/5 is frequently totally overlooked, yet any time I sub in mallet for mog's I notice it big time when I'm taking objectives after teamfights or trying to be a buffer for my team during poke battles.
That being said, I still agree with situational Mallet rush on Noct, but it's purely because of the convenience of the items on him. The midgame phage is BRUTAL on Noct (because of his built-in AS for proc consistency and MS on trail to stick long enough to get a proc), and he still needs more HP after it, making Mallet a very natural transition. I prefer wriggle's -> hog (and sometimes avarice too if I farm like a boss) -> phage -> atma's -> ghostblade + omen if I can on noct and then I either make mallet my last priority or sell phage for IE like a boss, but if your early income isn't happening and you need a faster power spike instead of gold/10, fast mallet makes a lot of sense.