the only thing about airdrops is that many people are involved in this. By definition therefore you usually won't get a big portion of the overall distribution (the more users sign up for the airdrop the less coins you will receive). This kind of sucks, but is by no means something that is not profitable. Even a couple of hundred dollars can multiply by a lot if the project will get ground and more people invest in it. Just try to look for good projects and you should be fine.