I have not summoned a djinn, but I've heard that while they do grant wishes they can be VERY tricky. It's recommended that you don't summon them. They tend to take the "be careful what you wish for" saying a bit far. Don't quote me on it, though, since I'm not very educated in this. I suggest doing some research.
They do are Real, though not all believe so.. But i bet it it's not like Alladin!
They are just same as if a demon or an angel, they might have free will or not, some may just be as friends to talk via Ouija board or Astral, while some hate humans and so cause trouble if summoned. (Warned if new)