You can become dependent on anything you enjoy. As for people developing HPPD from I-Doser, it is unknown what causes HPPD, so theres no telling why they got it, but its really rare, so don't worry. As for psychological harm, of course it can cause that, its called a bad trip. Its the risk you take.
sorry for digging up old post but heres something i read in an article a while ago.
watching, listening, reading pornography releases the same chemicals in your brain as if you were taking cocaine (not i-dose cocaine but ACTUAL cocaine)