First off, about superiority to 5HTP and L-Tryptophan, definitely a superior sleepaid because L-Tryptophan->5HTP->serotonin->melatonin.
I've always been an insomniac, and taking melatonin definitely helped at first(around 1.5-2 mg). I got the nice chewable peppermint 500mcg ones, taste like candy. Unfortunately I ended up popping them like candy too because you can quickly build up a tolerance, and I increased to around 7.5 mg daily. Def deep, uninterrupted(unless something actually interrupted) sleep, wake up feeling nice if you get the 8 hours or so. More dreamy.
If you find yourself building a tolerance back off it totally for a bit would be my advice. The good news is it's not damaging, your body just stops making as much because it doesn't think it needs to, so no lasting damage, but right as you drop off it, you'll have trouble getting to sleep again. Other than that no withdrawal symptoms or anything nasty like opiates.
I think the sleep tolerance is somewhat general, though switching sleep aids does help, but only to a certain point. At one point after 2 days with like 2 hours of sleep right I ended up taking quite a number of valerian root pills, several cups of rather strong valerian root tea(I brewed it from actual roots, not like just a bedtime tea or anything), a few pain killers(Not for sleeping, but achieved the affect usually), and about 8mg of melatonin and I couldn't get to sleep. So my advice would definitely be back off it after a while. However I find it very useful for random sleepless nights, and especially useful for travelling and shifting timezones. Or if you need to go to sleep immediately for something after whatever period of time.