Derivatives require a legal system that forces people to pay their debts and counter-parties strong enough to pay them.
From the Bitoption FAQ
"Is this Escrowed trading? YES. You are guaranteed to be able to execute once you've purchased a contract."
That's good enough for me.
Umm...I was reading the bitoption status thread earlier and it sounds like the owner has stopped responding, people are owed money etc.
A guarantee is only as good as the person making it. And an escrow is only worthwhile if it is by a trusted and reliable third party.