Airdrops are profitable, yes. They will be the easiest tokens you will ever make.
How hard can a sign up be? If you dont mind the ICO collecting some information, a piece of advice, make a new email account and a seperate wallet too.
No, they are a waste of time, i would never join an airdrop since you need to do a lot of things in order to join.. Nowadays, they ask you to join Twitter, Telegram, and a few other tasks, it is not worth it,.