I'd be careful with the methodology here. There's been research that shows that most melatonin supplements are megadosed, with something like the "physiological dosage range" being 1 - 2 micrograms (ug.) So I'd hope the researchers got a trustworthy source for their tablets. It seems to me that with such a low dosage range you don't have much margin to avoid errors.
I think when it comes to sleep problems the worst possible place to start is with pills. Pills quickly lead to dependence and a lot of them either stop working or introduce so many side effects that there's little "therapeutic benefit." I think the right approach for insomnia is to focus on improving overall health. A lot of symptoms people go to the doctor for in that category are due to life-style factors. So if you maintain healthy habits you don't have to end up on 10 different pills just to function...
It's a slippery slope, trust me on that.