For those of you who do take them: Aren't you concerned by side effects and/or long term health effects? Not judging, just genuinely curious; I've looked into them but it seems the general consensus is that their effects, both short and long term, are not very well understood yet.
I've considered a lot of others as well (e.g. *racetams - avoided on reports of 'brain fog' and a few of mental impairment - scary!). However, out of the dozens(?) I ended up considering, Modafinil was the only one I ended up deciding to try and ultimately take regularly.
I've read enough studies (and try to keep up to date) to know what our current knowledge about it is. In almost all of the studies, side-effects have been fairly standard (headaches, a few people getting sick, etc.). It's been used on-prescription for the past decade without seeing any uproar.
In the long-term, I consider the risk of unknowns worth the reward. Most evidence points to it being fairly safe, if not, that's a gamble I might pay for.
I drink alcohol to have fun, often to excess. I eat junk food. I actively choose to do a lot of things that shorten my lifespan for negligible returns.
If this little magic pill, which costs the same as a bottle of coca cola, makes me feel motivated and alert for 14 hours a day, I'm going to take it until I find a reason not to.