I used it for well over a year, but I noticed I was always disabling it as soon as it turned on. Eventually, I realised that having an accurate, carefully-calibrated display was pointless if I was going to use f.lux.
I tentatively tried using melatonin tablets instead, and I've found it works really well for me. Set an alarm for about 30-40 minutes before you want to go to sleep, take the tablet (sublingually) when the alarm goes off, and you'll notice you start feeling sleepy right about when you need to fall asleep.
Obviously, this kind of exogenous melatonin intake can only crudely approximate the curves for plasma melatonin levels resulting from endogenous production in the presence of zero artificial light, but using f.lux only removes one source of blue light. Sure, you might feel sleepy staring at your screen, but blue light inhibits melatonin synthesis so strongly you could turn on your bedroom light and have your melatonin production bottom out. IIRC, you can significantly attenuate melatonin production with light levels of ~100 lx, which is comparable to a really dim room. Good luck getting ready for bed in complete darkness.
You also need to titrate your dosage to find the right levels. For me, 0.2-0.5mg is all I need to achieve the necessary sleepiness to motivate me to get to sleep. I can take more with no noticeable effects, but I know others who report headaches the morning after. Also note that the older you are, the less melatonin you need.