The hike and the 11 km distance are definitely worth the view and the experience. Just as all the other posts say, bring water, comfortable shoes and not so much weight. Interesting fact, for the people coming from Oia as we did it is more challenging as it goes uphill rather than for those who are coming from For a to Oia which is easier. There are some places that go up and down but it is easier to come from For a to Oia than to go from Oia to For a. Anyways, you can always take the bus to either cities once you finish the circuit for 1.80 euros per person and the bus leaves both towns every 30 mins.
I was only sorry to see how it is an attraction that needs maintenance and also to be cleaned as I had to pick some of the garbage on my way to Fira. I love hiking but I hate it when people don't use the trash cans. You couldn't find any here but there is no need to throw the garbage anywhere. More